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Challenging Problem (challenging + problem)
Selected AbstractsSnap: A time critical decision-making framework for MOUT simulationsCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2008Shang-Ping Ting Abstract Deliberative reasoning based on the rational analysis of various alternatives often requires too much information and may be too slow in time critical situations. In these situations, humans rely mainly on their intuitions rather than some structured decision-making processes. An important and challenging problem in Military Operations on Urban Terrain (MOUT) simulations is how to generate realistic tactical behaviors for the non-player characters (also known as bots), as these bots often need to make quick decisions in time-critical and uncertain situations. In this paper, we describe our work on Snap, a time critical decision-making framework for the bots in MOUT simulations. The novel features of Snap include case-based reasoning (CBR) and thin slicing. CBR is used to make quick decisions by comparing the current situation with past experience cases. Thin slicing is used to model human's ability to quickly form up situation awareness under uncertain and complex situations using key cues from partial information. To assess the effectiveness of Snap, we have integrated it into Twilight City, a virtual environment for MOUT simulations. Experimental results show that Snap is very effective in generating quick decisions during time critical situations for MOUT simulations. Copyright © 2008 John Wiley & Sons, Ltd. [source] Automatic Facsimile of Chinese Calligraphic WritingsCOMPUTER GRAPHICS FORUM, Issue 7 2008Songhua Xu Abstract To imitate personal handwritings is non-trivial. In this paper, we attempt to address the challenging problem of automatic handwriting facsimile. We focus on Chinese calligraphic writings due to their rich variation in style, high artistic values and also the fact that they are among the most difficult candidates for the problem. We first analyze the structures and shapes of the constituent components, i.e., strokes and radicals, of characters in sample calligraphic writings by the same writer. To generate calligraphic writing in the style of the writer, we facsimile the individual character elements as well as the layout relationships used to compose the character, both in the writer's personal writing style. To test our algorithm, we compare our facsimileing results of Chinese calligraphic writings with the original writings. Our results are found to be acceptable for most cases, some of which are difficult to differentiate from the real ones. More results and supplementary materials are provided in our project website at http://www.cs.hku.hk/~songhua/facsimile/. [source] Efficacy of tropisetron in patients with advanced non-small-cell lung cancer receiving adjuvant chemotherapy with carboplatin and taxanesEUROPEAN JOURNAL OF CANCER CARE, Issue 2 2008N. TSAVARIS md Even though significant progress has been made, chemotherapy-induced emesis remains a challenging problem. Few studies focus on emesis in patients treated with carboplatin and the observation period is limited to the initial 24 h following chemotherapy. Thus, we investigated if tropisetron (T) monotherapy can adequately prevent acute and delayed emesis in non-small-cell lung cancer (NSCLC) patients receiving a moderately emetogenic chemotherapy (MEC) (carboplatin-containing) regimen. Furthermore, we explored the merits of adding dexamethasone (D) or alprazolam (A) to T, especially in the setting of a pre-existing high level of stress. We studied 60 patients with advanced NSCLC receiving carboplatin and taxanes in three consecutive cycles. During the first cycle, patients received 5 mg of T intravenously before chemotherapy and the same dose per os on each of the following 3 days. In the second cycle, T was co-administered with 8 mg of D once a day, while, during the third cycle, T was combined with per os A 0.25 mg every 12 h and continued over the following 3 days. Finally, we evaluated the impact of stress on the anti-emetic response achieved with the previously described regimens. The combination of T + A was superior to T monotherapy and the combination of T + D, regarding the prevention of acute and delayed emesis. Both T + A and T + D combinations led to appetite improvement, while patients receiving T + A experienced sedation more frequently. Interestingly, subgroup analysis revealed that patients without underlying stress obtained no further benefit by the addition of A or D, while both T + A and T + D combinations led to a better anti-emetic response in patients with stress. In conclusion, T monotherapy provides a satisfactory result in controlling nausea and emesis caused by a MEC regimen in patients without stress. However, the addition of D and, mainly, A improves its anti-emetic effect in patients with obvious stress. [source] Prioritisation of data partitioned MPEG,4 video over mobile networks,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2001Stewart T. Worrall Despite much research in the field of mobile multimedia, delivery of real,time,interactive video over noisy wireless channels remains a challenging problem. Two of the major issues in providing true end,to,end mobile multimedia capability are interoperability between platforms and networks and the poor performance of video compression algorithms in error,prone environments. This paper presents a method for prioritising data partitioned MPEG,4 video in a way suitable for transmission over a mobile network. The effectiveness of the technique is demonstrated by examining the performance when transmitted using the Real,Time Transport protocol over GPRS (General Packet Radio Service) data channels under varying channel conditions. [source] The role of stem cells in suppurative environmentsEXPERIMENTAL DERMATOLOGY, Issue 6 2006Dolores Herreros Purpose:,The management of suppurative perianal lesions presents an extremely challenging problem. Stem cells (SC) extracted from certain tissues, such as adipose tissue, can differentiate into various cell types. Therefore, we have tried to use such cells to stimulate healing in a purulent environment. Methods:,In the beginning, we designed a phase I clinical trial, involving five patients with Crohn's disease. We inoculated nine fistulas in four patients with autologous adipose-derived stem cells (ADSC) and were followed at least 8 weeks. Seventy-five percent became healed, and 25% showed a decrease in output flow. No adverse effects were observed in any patient. This study evidenced that such cells are safe. Then, we started a research line using SC in different suppurative environments. During the course of these studies, we had the opportunity to treat a patient with perianal hidradenitis suppurativa using our current protocol of ADSC transplantation. Eight weeks after injection, patient had no perianal suppuration, and a year later remains well. Discussion:,The biological mechanism that underlies the therapeutic success of ADSC transplantation is unknown. Cell differentiation, secretion of growth factors or immunomodulatory effects have been suggested. No ethical conflicts were identified by our Ethics Committee, because the cells were autologous. Conclusions:,Our study shows that ADSC are safe for the treatment of suppurative processes. The actual number of patients included and the uncontrolled nature of these pilot studies do not allow demonstration of the effectiveness of the treatment. However, the results encourage the performance of further studies. [source] Contiguity Constraints for Single-Region Site Search ProblemsGEOGRAPHICAL ANALYSIS, Issue 4 2000Thomas J. Cova This paper proposes an explicit set of constraints as a general approach to the contiguity problem in site search modeling. Site search models address the challenging problem of identifying the best area in a study region for a particular land use, given that there are no candidate sites. Criteria that commonly arise in a search include a site's area, suitability, cost, shape, and proximity to surrounding geographic features. An unsolved problem in this modeling arena is the identification of a general set of mathematical programming constraints that can guarantee a contiguous solution (site) for any 0,1 integer-programming site search formulation. The constraints proposed herein address this problem, and we evaluate their efficacy and efficiency in the context of a regular and irregular tessellation of geographic space. An especially efficient constraint form is derived from a more general form and similarly evaluated. The results demonstrate that the proposed constraints represent a viable, general approach to the contiguity problem. [source] Delineating the rupture planes of an earthquake doublet using Source-Scanning Algorithm: application to the 2005 March 3 Ilan Doublet, northeast TaiwanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010Chih-Wen Kan SUMMARY Correct identification of the fault plane(s) associated with an earthquake doublet is a very challenging problem because the pair of events often occurs in close space and time with almost the same magnitude. Most long-period waveforms of an earthquake doublet are severely tangled and thus unsuitable for conventional waveform inversion methods. In this study, we try to resolve this issue by utilizing the recently developed Source-Scanning Algorithm (SSA). The SSA systematically searches the model space for seismic sources whose times and locations are most compatible with the observed arrivals of large amplitudes on seismograms. The identification of a seismic source is based on the brightness function, which is defined as the summation of the normalized waveform amplitudes at the predicted arrival times at all stations. By illuminating the spatiotemporal distribution of asperities during an earthquake's source process, we are able to constrain the orientation of the rupture propagation that, in turn, leads to the identification of the fault plane. A series of synthetic experiments are performed to test SSA's resolution under various scenarios including different directions of rupture propagation, imperfect station coverage and short origin time difference between the two events of a doublet. Because only short-period records are needed in the analysis, the proposed method is best suited for an earthquake doublet with a short time gap between the two events. Using the 2005 Ilan doublet (the origin time difference is only 70 s) that occurred in northeast Taiwan as an example, we show that the trace of the brightest spots moves towards the west and infer the E,W-striking plane to be the actual fault plane. [source] Recurrent pleomorphic adenoma of the parotid gland: Analysis of 108 consecutive patientsHEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 9 2007Claus Wittekindt MD Abstract Background Surgery for recurrent parotid pleomorphic adenoma is a challenging problem. Methods One hundred eight patients who underwent 134 reoperations for recurrent parotid pleomorphic adenoma (follow-up, 22 years) were evaluated for histopathologic features and risk factors for recurrence. Results The number of reoperations for tumor recurrence ranged from 1 to 10. Twenty-seven patients (25%) developed permanent facial nerve weakness. The risks for clinically evident rerecurrence after 1, 5, and 15 years were 16%, 42%, and 75%, respectively. Female sex, young age at initial treatment, and enucleation instead of parotidectomy for treatment of the first recurrence were significant risk factors for rerecurrence. The mean number of recurrent tumor nodules was 26. Conclusions Surgery for recurrent parotid pleomorphic adenoma has a high rate of facial nerve morbidity. The chance of rerecurrence is high. Extended parotidectomy seems to be the best approach for the reoperation to reduce the risk of rerecurrence. © 2007 Wiley Periodicals, Inc. Head Neck 2007 [source] Soft Decision with Soft Target for Car-like Mobile Vehicle in Dynamic EnvironmentIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2009Yougen Chen Non-member Abstract Online flexible operation of a car-like mobile vehicle with non-holonomic constraints in dynamic environment is still a very challenging problem because the surrounding situations are not qualified in static, knowledge is only partial and the execution is often associated with uncertainty. The difficulty lies in the setting of appropriate moving sub-targets in real-time to obtain a collision-free and low-cost path. In this paper, we present a new approach for the autonomous motion control of mobile vehicle in a narrow area with static and dynamic obstacles. It is based on the selection of sub-target points of vehicle's movement called ,soft target' which is a target set defined as all possible and reachable via-points in a navigation space. The soft target is acquired by online learning based on the final target and environment information. Each element of it has its membership value in [0, 1] denoting its evaluation degree. With the acquired soft target, soft decision is made like human's decision process by predictive fuzzy control (PFC) to achieve final target safely and economically. The simulation results show the effectiveness and flexibility of the proposed vehicle motion control method. © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Non-locking tetrahedral finite element for surgical simulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2009Grand Roman Joldes Abstract To obtain a very fast solution for finite element models used in surgical simulations, low-order elements, such as the linear tetrahedron or the linear under-integrated hexahedron, must be used. Automatic hexahedral mesh generation for complex geometries remains a challenging problem, and therefore tetrahedral or mixed meshes are often necessary. Unfortunately, the standard formulation of the linear tetrahedral element exhibits volumetric locking in case of almost incompressible materials. In this paper, we extend the average nodal pressure (ANP) tetrahedral element proposed by Bonet and Burton for a better handling of multiple material interfaces. The new formulation can handle multiple materials in a uniform way with better accuracy, while requiring only a small additional computation effort. We discuss some implementation issues and show how easy an existing Total Lagrangian Explicit Dynamics algorithm can be modified in order to support the new element formulation. The performance evaluation of the new element shows the clear improvement in reaction forces and displacements predictions compared with the ANP element in case of models consisting of multiple materials. Copyright © 2008 John Wiley & Sons, Ltd. [source] DSC-Ritz method for high-mode frequency analysis of thick shallow shellsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2005C. W. Lim Abstract This paper addresses a challenging problem in computational mechanics,the analysis of thick shallow shells vibrating at high modes. Existing methods encounter significant difficulties for such a problem due to numerical instability. A new numerical approach, DSC-Ritz method, is developed by taking the advantages of both the discrete singular convolution (DSC) wavelet kernels of the Dirichlet type and the Ritz method for the numerical solution of thick shells with all possible combinations of commonly occurred boundary conditions. As wavelets are localized in both frequency and co-ordinate domains, they give rise to numerical schemes with optimal accurate, stability and flexibility. Numerical examples are considered for Mindlin plates and shells with various edge supports. Benchmark solutions are obtained and analyzed in detail. Experimental results validate the convergence, stability, accuracy and reliability of the proposed approach. In particular, with a reasonable number of grid points, the new DSC-Ritz method is capable of producing highly accurate numerical results for high-mode vibration frequencies, which are hitherto unavailable to engineers. Moreover, the capability of predicting high modes endows us the privilege to reveal a discrepancy between natural higher-order vibration modes of a Mindlin plate and those calculated via an analytical relationship linking Kirchhoff and Mindlin plates. Copyright © 2004 John Wiley & Sons, Ltd. [source] A two-grid fictitious domain method for direct simulation of flows involving non-interacting particles of a very small sizeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010A. Dechaume Abstract The full resolution of flows involving particles whose scale is hundreds or thousands of times smaller than the size of the flow domain is a challenging problem. A naive approach would require a tremendous number of degrees of freedom in order to bridge the gap between the two spatial scales involved. The approach used in the present study employs two grids whose grid size fits the two different scales involved, one of them (the micro-scale grid) being embedded into the other (the macro-scale grid). Then resolving first the larger scale on the macro-scale grid, we transfer the so obtained data to the boundary of the micro-scale grid and solve the smaller size problem. Since the particle is moving throughout the macro-scale domain, the micro-scale grid is fixed at the centroid of the moving particle and therefore moves with it. In this study we combine such an approach with a fictitious domain formulation of the problem resulting in a very efficient algorithm that is also easy to implement in an existing CFD code. We validate the method against existing experimental data for a sedimenting sphere, as well as analytical results for motion of an inertia-less ellipsoid in a shear flow. Finally, we apply the method to the flow of a high aspect ratio ellipsoid in a model of a human lung airway bifurcation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Efficient video retrieval using index structureINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2-3 2008Jing Zhang Abstract Video retrieval remains a challenging problem since most of traditional query algorithms are ineffectual and time-consuming. In this article, we proposed a new video retrieval method, which segments the video stream by visual similarity between neighboring frames, and adopt the high-dimensional index structure to organize segments. Furthermore, a new similarity measure is brought forward to improve the query accuracy by synthetically taking into account the visual similarity and temporal order among video segments. Based on the similarity measure, we propose a novel video clip retrieval algorithm which achieves high query efficiency by using restricted sliding window to construct candidate video clips. Experimental results show that the proposed video retrieval method is efficient and effective. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 18, 113,123, 2008 [source] Formation of simple organic molecules in the interstellar mediumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2008Abraham F. Jalbout Abstract In this work we present a methodology for the synthesis of simple molecules from basic formaldehyde (H2CO) precursors. We have approached this challenging problem by considering a basic dimerization scheme that eventually leads to diose and methyl formate, using an HCO+ proton source. This species was chosen due to its ample abundance in the atmosphere. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Protein folding simulations: From coarse-grained model to all-atom modelIUBMB LIFE, Issue 6 2009Jian Zhang Abstract Protein folding is an important and challenging problem in molecular biology. During the last two decades, molecular dynamics (MD) simulation has proved to be a paramount tool and was widely used to study protein structures, folding kinetics and thermodynamics, and structure,stability,function relationship. It was also used to help engineering and designing new proteins, and to answer even more general questions such as the minimal number of amino acid or the evolution principle of protein families. Nowadays, the MD simulation is still undergoing rapid developments. The first trend is to toward developing new coarse-grained models and studying larger and more complex molecular systems such as protein,protein complex and their assembling process, amyloid related aggregations, and structure and motion of chaperons, motors, channels and virus capsides; the second trend is toward building high resolution models and explore more detailed and accurate pictures of protein folding and the associated processes, such as the coordination bond or disulfide bond involved folding, the polarization, charge transfer and protonate/deprotonate process involved in metal coupled folding, and the ion permeation and its coupling with the kinetics of channels. On these new territories, MD simulations have given many promising results and will continue to offer exciting views. Here, we review several new subjects investigated by using MD simulations as well as the corresponding developments of appropriate protein models. These include but are not limited to the attempt to go beyond the topology based G,-like model and characterize the energetic factors in protein structures and dynamics, the study of the thermodynamics and kinetics of disulfide bond involved protein folding, the modeling of the interactions between chaperonin and the encapsulated protein and the protein folding under this circumstance, the effort to clarify the important yet still elusive folding mechanism of protein BBL, the development of discrete MD and its application in studying the ,,, conformational conversion and oligomer assembling process, and the modeling of metal ion involved protein folding. © 2009 IUBMB IUBMB Life, 61(6): 627,643, 2009 [source] Estimating risk aversion from ascending and sealed-bid auctions: the case of timber auction dataJOURNAL OF APPLIED ECONOMETRICS, Issue 7 2008Jingfeng Lu Estimating bidders' risk aversion in auctions is a challenging problem because of identification issues. This paper takes advantage of bidding data from two auction designs to identify nonparametrically the bidders' utility function within a private value framework. In particular, ascending auction data allow one to recover the latent distribution of private values, while first-price sealed-bid auction data allow one to recover the bidders' utility function. This leads to a nonparametric estimator. An application to the US Forest Service timber auctions is proposed. Estimated utility functions display concavity, which can be partly captured by constant relative risk aversion. Copyright © 2008 John Wiley & Sons, Ltd. [source] Using support vector machines for prediction of protein structural classes based on discrete wavelet transformJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2009Jian-Ding Qiu Abstract The prediction of secondary structure is a fundamental and important component in the analytical study of protein structure and functions. How to improve the predictive accuracy of protein structural classification by effectively incorporating the sequence-order effects is an important and challenging problem. In this study, a new method, in which the support vector machine combines with discrete wavelet transform, is developed to predict the protein structural classes. Its performance is assessed by cross-validation tests. The predicted results show that the proposed approach can remarkably improve the success rates, and might become a useful tool for predicting the other attributes of proteins as well. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Using pseudo amino acid composition to predict protein structural classes: Approached with complexity measure factorJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2006Xuan Xiao Abstract The structural class is an important feature widely used to characterize the overall folding type of a protein. How to improve the prediction quality for protein structural classification by effectively incorporating the sequence-order effects is an important and challenging problem. Based on the concept of the pseudo amino acid composition [Chou, K. C. Proteins Struct Funct Genet 2001, 43, 246; Erratum: Proteins Struct Funct Genet 2001, 44, 60], a novel approach for measuring the complexity of a protein sequence was introduced. The advantage by incorporating the complexity measure factor into the pseudo amino acid composition as one of its components is that it can catch the essence of the overall sequence pattern of a protein and hence more effectively reflect its sequence-order effects. It was demonstrated thru the jackknife crossvalidation test that the overall success rate by the new approach was significantly higher than those by the others. It has not escaped our notice that the introduction of the complexity measure factor can also be used to improve the prediction quality for, among many other protein attributes, subcellular localization, enzyme family class, membrane protein type, and G-protein couple receptor type. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 478,482, 2006 [source] Automatic guidance of a four-wheel-steering mobile robot for accurate field operationsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 6-7 2009Christophe Cariou As world population growth requires an increasing level of farm production at the same time that environmental preservation is a priority, the development of new agricultural tools and methods is required. In this framework, the development of robotic devices can provide an attractive solution, particularly in the field of autonomous vehicles. Accurate automatic guidance of mobile robots in farming constitutes a challenging problem for researchers, mainly due to the low grip conditions usually found in such a context. From assisted-steering systems to agricultural robotics, numerous control algorithms have been studied to achieve high-precision path tracking and have reached an accuracy within ±10 cm, whatever the ground configuration and the path to be followed. However, most existing approaches consider classical two-wheel-steering vehicles. Unfortunately, by using such a steering system, only the lateral deviation with respect to the path to be followed can be satisfactorily controlled. Indeed, the heading of the vehicle remains dependent on the grip conditions, and crabwise motions, for example, are systematically observed on a slippery slope, leading to inaccurate field operations. To tackle this drawback, a four-wheel-steering (4WS) mobile robot is considered, enabling servo of both lateral and angular deviations with respect to a desired trajectory. The path tracking control is designed using an extended kinematic representation, allowing account to be taken online of wheel skidding, while a backstepping approach permits management of the 4WS structure. The result is an approach taking advantage of both rear and front steering actuations to fully compensate for sliding effects during path tracking. Moreover, a predictive algorithm is developed in order to address delays induced by steering actuators, compensating for transient overshoots in curves. Experimental results demonstrate that despite sliding phenomena, the mobile robot is able to automatically and accurately achieve a desired path, with lateral and angular errors, respectively, within ±10 cm and ±2 deg, whatever its shape and whatever the terrain conditions. This constitutes a promising result in efforts to define efficient tools with which to tackle tomorrow's agriculture challenge. © 2009 Wiley Periodicals, Inc. [source] PRELIMINARY EVALUATION OF THE APPLICATION OF THE FTIR SPECTROSCOPY TO CONTROL THE GEOGRAPHIC ORIGIN AND QUALITY OF VIRGIN OLIVE OILSJOURNAL OF FOOD QUALITY, Issue 4 2007ALESSANDRA BENDINI ABSTRACT A rapid Fourier transform infrared (FTIR) attenuated total reflectance spectroscopic method was applied to determine qualitative parameters such as free fatty acid (FFA) content and the peroxide value (POV) in virgin olive oils. Calibration models were constructed using partial least squares regression on a large number of virgin olive oil samples. The best results (R2 = 0.955, root mean square error in cross validation [RMSECV] = 0.15) to evaluate FFA content expressed in oleic acid % (w/w) were obtained considering a calibration range from 0.2 to 9.2% of FFA relative to 190 samples. For POV determination, the result obtained, built on 80 olive oil samples with a calibration range from 11.1 to 49.7 meq O2/kg of oil, was not satisfactory (R2 = 0.855, RMSECV = 3.96). We also investigated the capability of FTIR spectroscopy, in combination with multivariate analysis, to distinguish virgin olive oils based on geographic origin. The spectra of 84 monovarietal virgin olive oil samples from eight Italian regions were collected and elaborated by principal component analysis (PCA), considering the fingerprint region. The results were satisfactory and could successfully discriminate the majority of samples coming from the Emilia Romagna, Sardinian and Sicilian regions. Moreover, the explained variance from this PCA was higher than 96%. PRACTICAL APPLICATIONS The verification of the declared origin or the determination of the origin of an unidentified virgin olive oil is a challenging problem. In this work, we have studied the applicability of Fourier transform infrared coupled with multivariate statistical analysis to discriminate the geographic origin of virgin olive oil samples from different Italian regions. [source] Evidence-based algorithms for diagnosing and treating ventilator-associated pneumonia,JOURNAL OF HOSPITAL MEDICINE, Issue 5 2008Richard J. Wall MD Abstract BACKGROUND: Ventilator-associated pneumonia (VAP) is widely recognized as a serious and common complication associated with high morbidity and high costs. Given the complexity of caring for heterogeneous populations in the intensive care unit (ICU), however, there is still uncertainty regarding how to diagnose and manage VAP. OBJECTIVE: We recently conducted a national collaborative aimed at reducing health care,associated infections in ICUs of hospitals operated by the Hospital Corporation of America (HCA). As part of this collaborative, we developed algorithms for diagnosing and treating VAP in mechanically ventilated patients. In the current article, we (1) review the current evidence for diagnosing VAP, (2) describe our approach for developing these algorithms, and (3) illustrate the utility of the diagnostic algorithms using clinical teaching cases. DESIGN: This was a descriptive study, using data from a national collaborative focused on reducing VAP and catheter-related bloodstream infections. SETTING: The setting of the study was 110 ICUs at 61 HCA hospitals. INTERVENTION: None. MEASUREMENTS AND RESULTS: We assembled an interdisciplinary team that included infectious disease specialists, intensivists, hospitalists, statisticians, critical care nurses, and pharmacists. After reviewing published studies and the Centers for Disease Control and Prevention VAP guidelines, the team iteratively discussed the evidence, achieved consensus, and ultimately developed these practical algorithms. The diagnostic algorithms address infant, pediatric, immunocompromised, and adult ICU patients. CONCLUSIONS: We present practical algorithms for diagnosing and managing VAP in mechanically ventilated patients. These algorithms may provide evidence-based real-time guidance to clinicians seeking a standardized approach to diagnosing and managing this challenging problem. Journal of Hospital Medicine 2008;3:409,422. © 2008 Society of Hospital Medicine. [source] Planning models for parallel batch reactors with sequence-dependent changeoversAICHE JOURNAL, Issue 9 2007Muge Erdirik-Dogan Abstract In this article we address the production planning of parallel multiproduct batch reactors with sequence-dependent changeovers, a challenging problem that has been motivated by a real-world application of a specialty chemicals business. We propose two production planning models that anticipate the impact of the changeovers in this batch processing problem. The first model is based on underestimating the effects of the changeovers that leads to an MILP problem of moderate size. The second model incorporates sequencing constraints that yield very accurate predictions, but at the expense of a larger MILP problem. To solve large scale problems in terms of number of products and reactors, or length of the time horizon, we propose a decomposition technique based on rolling horizon scheme and also a relaxation of the detailed planning model. Several examples are presented to illustrate the performance of the proposed models. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Thyroid hormone enhances transected axonal regeneration and muscle reinnervation following rat sciatic nerve injuryJOURNAL OF NEUROSCIENCE RESEARCH, Issue 8 2010Petrica-Adrian Panaite Abstract Improvement of nerve regeneration and functional recovery following nerve injury is a challenging problem in clinical research. We have already shown that following rat sciatic nerve transection, the local administration of triiodothyronine (T3) significantly increased the number and the myelination of regenerated axons. Functional recovery is a sum of the number of regenerated axons and reinnervation of denervated peripheral targets. In the present study, we investigated whether the increased number of regenerated axons by T3-treatment is linked to improved reinnervation of hind limb muscles. After transection of rat sciatic nerves, silicone or biodegradable nerve guides were implanted and filled with either T3 or phosphate buffer solution (PBS). Neuromuscular junctions (NMJs) were analyzed on gastrocnemius and plantar muscle sections stained with rhodamine ,-bungarotoxin and neurofilament antibody. Four weeks after surgery, most end-plates (EPs) of operated limbs were still denervated and no effect of T3 on muscle reinnervation was detected at this stage of nerve repair. In contrast, after 14 weeks of nerve regeneration, T3 clearly enhanced the reinnervation of gastrocnemius and plantar EPs, demonstrated by significantly higher recovery of size and shape complexity of reinnervated EPs and also by increased acetylcholine receptor (AChRs) density on post synaptic membranes compared to PBS-treated EPs. The stimulating effect of T3 on EP reinnervation is confirmed by a higher index of compound muscle action potentials recorded in gastrocnemius muscles. In conclusion, our results provide for the first time strong evidence that T3 enhances the restoration of NMJ structure and improves synaptic transmission. © 2010 Wiley-Liss, Inc. [source] Classification and management of chronic sialadenitis of the parotid glandJOURNAL OF ORAL REHABILITATION, Issue 1 2009S. WANG Summary, Saliva has numerous oral functions and multiple functions in relation to digestion in the upper gastrointestinal tract. Chronic salivary hypofunction can lead to severe adverse health outcomes. Chronic sialadenitis is one of the major conditions that can cause salivary hypofunction. A correct diagnosis and management of chronic sialadenitis is essential for the recovery of salivary hypofunction. Chronic sialadenitis of the parotid gland is often seen in the clinic, sometimes also referred to as recurrent pyogenic parotitis, recurrent parotitis, non-obstructive parotitis, sialadenitis or obstructive parotitis, among other terms. The literature describes several different classifications and denominations for chronic sialadenitis of the parotid gland. These various classifications and denominations complicate the definition and diagnostic criteria, and if chronic sialadenitis of the parotid gland can develop into Sjogren's syndrome remains unclear. Treatment of this condition is also a challenging problem. Here, we review the presented classification and denomination of chronic sialadenitis of the parotid gland, proposing a classification based on the disease entities identified in a long-term follow-up investigation, and discuss the treatment principles for the condition. [source] Global gene profiling reveals a downregulation of BMP gene expression in experimental atrophic nonunions compared to standard healing fracturesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 7 2006Takahiro Niikura Abstract Nonunion is a challenging problem that may occur following certain bone fractures. However, there has been little investigation of the molecular basis of nonunions. Bone morphogenetic proteins (BMPs) play a significant role in osteogenesis. However, little is known about the expression patterns of BMPs in abnormal bone healing that results in nonunion formation. These facts prompted us to investigate and compare the gene expression patterns of BMPs and their antagonists in standard healing fractures and nonunions using rat experimental models. Standard closed healing fractures and experimental atrophic nonunions produced by periosteal cauterization at the fracture site were created in rat femurs. At postfracture days 3, 7, 10, 14, 21, and 28, total RNA was extracted from the callus of standard healing fracture and fibrous tissue of nonunion (n,=,4 per each time point and each group). Gene expression of BMPs, BMP antagonists, and other regulatory molecules were studied by methods including Genechip® microarray and real-time quantitative RT-PCR. Gene expression of BMP-2, 3, 3B, 4, 6, 7, GDF-5, 7, and BMP antagonists noggin, drm, screlostin, and BAMBI were significantly lower in nonunions compared to standard healing fractures at several time points. Downregulation in expression of osteogenic BMPs may account for the nonunions of fracture. The balance between BMPs and their endogenous antagonists is critical for optimal fracture healing. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1463,1471, 2006 [source] Challenge of synthetic celluloseJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2005Shiro Kobayashi Abstract This article focuses on why and how the chemical synthesis of cellulose was accomplished. The synthesis of cellulose was an important, challenging problem for half a century in polymer chemistry. For the synthesis, a new method of enzymatic polymerization was developed. A monomer of ,- D -cellobiosyl fluoride (,-CF) was designed and subjected to cellulase catalysis, which led to synthetic cellulose for the first time. Cellulase is a hydrolysis enzyme of cellulose; cellulase, inherently catalyzing the bond cleavage of cellulose in vivo, catalyzes the bond formation via the polycondensation of ,-CF in vitro. It is thought that the polymerization and hydrolysis involve a common intermediate (transition state). This view led us to a new concept, a transition-state analogue substrate, for the design of the monomer. The preparation of cellulase proteins with biotechnology revealed the enzymatic catalytic functions in the hydrolysis and polymerization to cellulose. High-order molecular structures were in situ formed and observed as fibrils (cellulose I) and spherulites (cellulose II). In situ small-angle neutron scattering measurements suggested a fractal surface formation of a synthetic cellulose assembly. The principle of cellulose synthesis was extended to the synthesis of other natural polysaccharides, such as xylan and amylose, and unnatural polysaccharides. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 693,710, 2005 [source] Affinity enhancement of an in vivo matured therapeutic antibody using structure-based computational designPROTEIN SCIENCE, Issue 5 2006Louis A. Clark Abstract Improving the affinity of a high-affinity protein,protein interaction is a challenging problem that has practical applications in the development of therapeutic biomolecules. We used a combination of structure-based computational methods to optimize the binding affinity of an antibody fragment to the I-domain of the integrin VLA1. Despite the already high affinity of the antibody (Kd ,7 nM) and the moderate resolution (2.8 Å) of the starting crystal structure, the affinity was increased by an order of magnitude primarily through a decrease in the dissociation rate. We determined the crystal structure of a high-affinity quadruple mutant complex at 2.2 Å. The structure shows that the design makes the predicted contacts. Structural evidence and mutagenesis experiments that probe a hydrogen bond network illustrate the importance of satisfying hydrogen bonding requirements while seeking higher-affinity mutations. The large and diverse set of interface mutations allowed refinement of the mutant binding affinity prediction protocol and improvement of the single-mutant success rate. Our results indicate that structure-based computational design can be successfully applied to further improve the binding of high-affinity antibodies. [source] Automatic design of conventional distillation column sequence by genetic algorithmTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Ramin Bozorgmehry Boozarjomehry Abstract Synthesis of the optimum conventional (with non-sharp separations) distillation column sequence (DCS) is a challenging problem, in the field of chemical process design and optimization, due to its huge search space and combinatorial nature. In this paper, a novel procedure for the synthesis of optimum Conventional Distillation Column Sequence is proposed. The proposed method is based on evolutionary algorithms. The main criterion used to screen alternative DCS's is the Total Annual Cost (TAC). In order to estimate the TAC of each DCS alternative all columns that exist in the DCS are designed using short-cut methods. The performance of the proposed method and other alternatives are compared based on the results obtained for four standard benchmark problems used by researchers working in this area. Based on the results of the comparison, the proposed method outperforms the other methods and is also more flexible than other existing methods. La synthèse de la séquence de colonne de distillation (SCD) traditionnelle optimale (caractérisée par des séparations non tranchantes) représente un problème difficile à régler, dans le domaine de la conception et de l'optimisation de procédés chimiques, en raison de son immense espace de recherche et de sa nature combinatoire. Ce document propose une procédure nouvelle en vue de la synthèse de la séquence de colonne de distillation traditionnelle optimale. La méthode proposée est fondée sur des algorithmes évolutionnistes. Le critère principal utilisé pour présélectionner les autres possibilités de SCD est le coût total annuel (CTA). Pour estimer le CTA de chaque option de SCD, toutes les colonnes qui existent dans la SCD sont conçues en utilisant des méthodes abrégées. On compare ensuite le rendement de la méthode proposée et des autres possibilités en s'appuyant sur les résultats obtenus dans le cadre de quatre problèmes d'évaluation standard utilisés par les chercheurs oeuvrant dans ce domaine. En s'appuyant sur les résultats de la comparaison, la méthode proposée donne un meilleur rendement que les autres méthodes et est également plus souple que les autres méthodes qui existent. [source] Trends in the management of severe acute pancreatitis: interventions and outcomeANZ JOURNAL OF SURGERY, Issue 5 2004Richard Flint Background: Severe acute pancreatitis (SAP) in the intensive care unit (ICU) is a complex and challenging problem. The aim of the present study was to identify trends in management of SAP patients admitted to a tertiary level ICU, and to relate these to changes in interventions and outcome. Methods: Patients admitted to the Department of Critical Care Medicine (DCCM), Auckland Public Hospital with SAP from 1988 to 2001 (inclusive) were identified from the DCCM prospective database, and data were extracted from several sources. Results: One hundred and twelve patients (men 69, women 43, mean age (±SD) 57.3 years ± 14.3) were admitted with SAP to DCCM in the 13-year period. Aetiology was gallstones (42%), alcohol (29%), or idiopathic (29%). At admission to DCCM the median duration of symptoms was 7 days (range 1,100) and the mean (±SD) Acute Physiology and Chronic Health Evaluation II score was 19.9 ± 8.2. Ninety-nine patients (88%) had respiratory failure and 79 (71%) had circulatory failure. The number of necrosectomies peaked between 1991 and 1995 (17/35 patients (49%) compared to 4/22 (18%) prior 1991; ,2 = 6.90, P = 0.032). Abdominal decompression, enteral nutrition, percutaneous tracheostomy, and the use of stents in endoscopic retrograde cholangiopancreatography were introduced over the study period. The length of stay in DCCM did not alter (median 4 days, range 1,60) but there was a reduction in the length of hospital stay (median 36 days to 15 days; anova= 6.16, P = 0.046). The overall mortality was 31% (35/112) and did not alter over the study period. Conclusions: SAP remains a formidable disease with a high mortality despite a number of changes in intensive care and surgical management. [source] Use of a retrograde femoral nail in a patient with McCune,Albright syndromeANZ JOURNAL OF SURGERY, Issue 12 2003John D. Garvan McCune,Albright Syndrome is a rare condition characterized by endocrine abnormalities, precocious puberty, pigmented skin lesions and polyostotic fibrous dysplasia with consequent fractures and limb deformity. Patients with this syndrome might have had multiple operations on a limb and might also have extensive internal fixation in-situ. We review the case of a 41-year-old woman with McCune,Albright syndrome, who presented with a pathological fracture of her left femur below a long plate and screws. Our management of this challenging problem included the use of a retrograde femoral nail, which, because of the need to retain pre-existing internal fixation, had to be locked proximally through a hole in a femoral plate. This technique, combined with reaming, and thus bone grafting of the fracture, and also perioperative infusions of pamidronate, allowed an early recovery and return to premorbid function for the patient. In the present study we detail our technique and discuss its advantages over other possible methods of treatment. [source] | |||||||||||||||||||||||||||||||