ACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2002
Thomas Oldfield
The interpretation of macromolecular crystallographic electron-density maps is a difficult and traditionally a manual step in the determination of a protein structure. The visualization of information within an electron-density map can be extremely arduous owing to the amount and complexity of information present. The ability to see the overall fold and structure of the molecule is usually lost among all the detail, particularly with larger structures. This paper describes a novel method of analysis of electron density in real space that can determine the secondary structure of a protein within minutes without any user intervention. The method is able to work with poor data as well as good data at resolutions down to 3.5,Å and is integral to the functionality of QUANTA. This article describes the methodology of the pattern recognition and its use with a number of sets of experimental data. [source]

Taking Stock at Quantum University,/INVENTAIRE À L'UNIVERSITÉ QUANTUM

ACCOUNTING PERSPECTIVES, Issue 4 2007
Gary Grudnitski
ABSTRACT This case describes the operations and procedures of a major university's athletic equipment room. It details the functions of requisitioning, purchasing, and receiving of equipment and gear used by the university's sports teams; and the custody, management, and record keeping of these items. On the basis of this description, the student is asked to prepare a two-part report. In the first part of the report the student should identify the weaknesses and associated risks that existed in the operations of the equipment room and its inventory of athletic equipment, gear, and clothing. Furthermore, instances in the case that provide evidence of these weaknesses and risks should also be reported. Upon receiving feedback on the adequacy of the first part of the report, the student in the second part of the report should delineate the controls that might be implemented to address these weaknesses and mitigate their associated risks. RÉSUMÉ Le cas élaboré par les auteurs contient une description du fonctionnement et des méthodes de gestion de la salle de matériel de sport d'une grande université. Les fonctions de demande d'achat, d'achat et de réception du matériel et des appareils utilisés par les équipes sportives de l'université y sont décrites avec précision, de même que celles de la garde et de la gestion de ce matériel ainsi que de la tenue des registres de stock. À partir de cette description, l'étudiant est appelé à préparer un rapport en deux volets. Dans le premier volet doivent être relevés les faiblesses que présentent le fonctionnement de la salle de matériel de sport et la tenue de l'inventaire du matériel, des appareils et des vêtements de sport, et les risques qui y sont associés. Les données du cas établissant l'existence de ces faiblesses et de ces risques doivent aussi figurer dans le rapport. Lorsque l'étudiant reçoit une appréciation de la pertinence du premier volet du rapport, il doit, dans le second volet, décrire les contrôles qui pourraient être mis en ,uvre pour combler ces faiblesses et atténuer les risques qui y sont associés. [source]

Performance of calibration standards for antigen quantitation with flow cytometry in chronic lymphocytic leukemia

CYTOMETRY, Issue 6 2007
Eva D. Rossmann
Abstract Background: The fluorescence intensities of CD3, CD4 on T cells and CD20, CD22 molecules on B cells were quantitatively measured on lymphocytes from chronic lymphocytic leukemia (CLL) patients and healthy donors. Methods: The performance of three different types of microbeads was compared, i.e. Quantum molecules of equivalent soluble fluorochrome (Q-MESF), Quantum simply cellular (QSC), and QuantiBRITEÔ (QB). As all PE-conjugates had a F/P ratio of 1:1, the MESF units represented also the antibody binding capacity (ABC). Results: The ABCs of CD4 and CD20 antigens estimated with QSC (ABCQSC) were higher than those assigned with QB (ABCQB) with an average difference 49%. Higher numbers of antigenic sites were obtained with Q-MESF than with QSC for CD20 antigen. On the contrary, CD4 antigenic sites numbers estimated with QSC were higher than those estimated with Q-MESF. ABC values estimated with Quantum MESF PE (ABCQ-MESF) were ,15% higher than ABCQSC, whereas ABCQ-MESF was ,49% higher than ABCQB. Statistically significant correlations were found between the values obtained using various standards. The present study is the first to report down-regulation of CD3 antigen on T cells from patients with CLL. Conclusions: This study emphasizes the relevance of quantitative measurement of fluorescence intensity by flow cytometry as a standardized approach to measure and interpret the expression of some CLL markers and reduce variability of results obtained at different sites in multi-center clinical studies. © 2007 Clinical Cytometry Society [source]

Distinguishing N -oxide and hydroxyl compounds: impact of heated capillary/heated ion transfer tube in inducing atmospheric pressure ionization source decompositions

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2004
Dilrukshi M. Peiris
Abstract In the pharmaceutical industry, a higher attrition rate during the drug discovery process means a lower drug failure rate in the later stages. This translates into shorter drug development time and reduced cost for bringing a drug to market. Over the past few years, analytical strategies based on liquid chromatography/mass spectrometry (LC/MS) have gone through revolutionary changes and presently accommodate most of the needs of the pharmaceutical industry. Among these LC/MS techniques, collision induced dissociation (CID) or tandem mass spectrometry (MS/MS and MSn) techniques have been widely used to identify unknown compounds and characterize metabolites. MS/MS methods are generally ineffective for distinguishing isomeric compounds such as metabolites involving oxygenation of carbon or nitrogen atoms. Most recently, atmospheric pressure ionization (API) source decomposition methods have been shown to aid in the mass spectral distinction of isomeric oxygenated (N -oxide vs hydroxyl) products/metabolites. In previous studies, experiments were conducted using mass spectrometers equipped with a heated capillary interface between the mass analyzer and the ionization source. In the present study, we investigated the impact of the length of a heated capillary or heated ion transfer tube (a newer version of the heated capillary designed for accommodating orthogonal API source design) in inducing for-API source deoxygenation that allows the distinction of N -oxide from hydroxyl compounds. 8-Hydroxyquinoline (HO-Q), quinoline- N -oxide (Q-NO) and 8-hydroxyquinoline- N -oxide (HO-Q-NO) were used as model compounds on three different mass spectrometers (LCQ Deca, LCQ Advantage and TSQ Quantum). Irrespective of heated capillary or ion transfer tube length, N -oxides from this class of compounds underwent predominantly deoxygenation decomposition under atmospheric pressure chemical ionization conditions and the abundance of the diagnostic [M + H , O]+ ions increased with increasing vaporizer temperature. Furthermore, the results suggest that in API source decompostion methods described in this paper can be conducted using mass spectrometers with non-heated capillary or ion transfer tube API interfaces. Because N-oxides can undergo in-source decomposition and interfere with quantitation experiments, particular attention should be paid when developing API based bioanalytical methods. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Quantum Well Intermixing Revolutionizes High Power Laser Diodes

LASER TECHNIK JOURNAL, Issue 5 2007
Monolithically integrated systems drive applications
Quantum well intermixing (QWI), an innovative monolithic integration platform, is changing the way diode lasers solve evolving optoelectronic needs , from high density, individually addressable laser arrays to high power laser products. QWI-enabled lasers deliver superior performance in terms of power, brightness, reliability, and yield, and are driving a revolution across market sectors including digital printing, defense, industrial, and medical imaging. [source]

Quantum and conversion efficiency calculation of AlGaAs/GaAs multiple quantum well solar cells

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2005
J. C. Rimada
Abstract The quantum well solar cell (QWSC) is a novel device that has been proposed by Barnham and co-workers at Imperial College London. In this work, the quantum efficiency for AlGaAs/GaAs QWSC has been calculated and compared with available data from the group at Imperial College London. Quantum efficiency calculations will be presented and compared with experimental data for several AlGaAs/GaAs QWSC, obtaining good agreement. The photocurrent then is calculated from the quantum efficiency calculations and included in the J(V) relation to optimize the efficiency of AlGaAs/GaAs QWSC. It also shows that for a range of quantum well widths and barrier bandgaps the conversion efficiencies of the quantum well solar cell are higher than the corresponding homogeneous p,i,n solar cell. Our results give a broad representation of quantum well solar cell operation, and provide a profitable guide for designing and interpreting the performance characteristics of AlGaAs/GaAs QWSCs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Quantum and thermal effects in the double exchange ferromagnet

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
N. Shannon
Abstract The physics of the ferromagnetic phase of the "double exchange" model has been widely discussed in the context of the CMR manganites. Usually, the double exchange ferromagnet is treated is classically, by mapping it onto an effective Heisenberg model. However this mapping does not permit a correct treatment of quantum or thermal fluctuation effects, and the results obtained lack many of the interesting features seen in experiments on the manganites. Here we outline a new analytic approach to systematically evaluating quantum and thermal corrections to the magnetic and electronic properties of the double exchange ferromagnet. [source]

Novel HVPE technology to grow nanometer thick GaN, AlN, AlGaN layers and multi-layered structures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Alexander Usikov
Abstract In this paper, we demonstrate new results on controllable HVPE growth of nitride materials with a deposition rate below 0.02 microns per minute and the first quantum size structures fabricated by HVPE. The nm-scale layer thicknesses were verified by transmision electron microscopy (TEM) and photoluminescence (PL). Quantum well (QW) GaN/AlGaN and AlN/AlGaN structures have been grown by HVPE for the first time. Properties of the HVPE grown QWs are reported. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Quantum dot-tagged microspheres for fluid-based DNA microarrays

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003
K. E. Meissner
Abstract Quantum dot-embedded microspheres offer a promising technology for the development of a fluid-based DNA microarray to replace current biochip microarray technology. The narrow emission and long lifetime from the quantum dots (QD's) is ideal for dense spectral multiplexing. Also, the QD's may all be excited by a single source. To implement this solution, we have fabricated CdSe quantum dots following published procedures and embedded them in polystyrene microspheres. As a first step in this development, we have investigated the use of a flow cytometer in analyzing the encoded microspheres. We demonstrate the use of a microsphere-based DNA detection system and investigate the readout of quantum dot-tagged microspheres. We also discuss some of the inherent limitations and difficulties of using such a system to address the need for a high-throughput readout for spectral multiplexing for fluid-based DNA microarrays. [source]

Increasing high-throughput Discovery bioanalysis using automated selected reaction monitoring compound optimization, ultra-high-pressure liquid chromatography, and single-step sample preparation workflows

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2009
James Smalley
QuickQuan is an integrated software package for Thermo Scientific triple quadrupole mass spectrometers that allows users to automate routine operations ranging from method development to data processing. QuickQuan automated optimization of compound-selected reaction monitoring (SRM) transitions by evaluating both positive and negative polarities during an infusion. Whichever mode produces the most intense Q1 scan is then carried to product ion spectra. QuickQuan then writes these SRM methods to a shared network database. The total volume of compound needed is 100,µL infused over approximately 1.6,min. The auto-optimization is carried out in 96-well plates and does not require an operator present. The SRM database was shared between two identical TSQ Quantum mass spectrometers. For data acquisition, QuickQuan automatically created a sequence file complete with a data processing method pre-populated with compound IDs and corresponding SRM transitions. To increase throughput we coupled each Finnigan Quantum with ultra-high-pressure liquid chromatography (uHPLC) accomplished using 4× Ultra Flux quaternary pumps that were designed to handle pressures up to 15 000,psi. The total run time for all analyses was 1.2,min using BEH 1.7,µm particle C18 columns. Further time reductions were realized with sample preparation accomplished using Strata Impact protein precipitation plates which provided an in-well protein crash and 0.20 micron filtering in a one-step process. Pharmacokinetic data turnaround time was significantly improved by combining these three techniques of automated method development with the speed efficiency of uHPLC and a single step in well sample preparation. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Quantum phase diagram for homogeneous Bose-Einstein condensate

ANNALEN DER PHYSIK, Issue 4 2005
H. Kleinert
Abstract We calculate the quantum phase transition for a homogeneous Bose gas in the plane of s -wave scattering length as and temperature T. This is done by improving a one-loop result near the interaction-free Bose-Einstein critical temperature Tc(0) with the help of recent high-loop results on the shift of the critical temperature due to a weak atomic repulsion based on variational perturbation theory. The quantum phase diagram shows a nose above Tc(0), so that we predict the existence of a reentrant transition above Tc(0), where an increasing repulsion leads to the formation of a condensate. [source]

The Historians' Disagreements over the Meaning of Planck's Quantum

CENTAURUS, Issue 3-4 2001
Olivier Darrigol
First page of article [source]

Radiologic measurements of the mandible: a comparison between CT-reformatted and conventional tomographic images

CLINICAL ORAL IMPLANTS RESEARCH, Issue 2 2004
Hanazawa Tomomi
Abstract: This study was carried out to compare the accuracy of determination of the mandibular contour and the position of the mandibular canal in cadaver mandibles by the multiplanar reconstruction method (MPR-CT), which has recently come to be used widely for preoperative examinations, with those by tomographic techniques and to evaluate the usefulness of MPR-CT. Using three imaging systems, i.e. Quantum CT scanner, Scanora, and OP-100, a total of 6 sites were scanned in the molar regions of 3 cadaver mandibles. The images obtained were measured twice each by 4 radiologists. The anatomic structures measured were the height and thickness of the mandible, distance from the alveolar crest to the mandibular canal, and distance from the buccal cortical bone to the mandibular canal. After scanning, the scanned areas of the mandibles were sliced at a thickness of 2 mm, and soft X-ray images of these slices were obtained. The values of the above 4 anatomic structures obtained by measurements in the soft X-ray radiograms using digital-display calipers were regarded as true values. When compared with the true values, the errors in the distance from the alveolar crest to the mandibular canal were within 1 mm (±1 mm) in 93.7% of the measurements by Direct-CT, 89.6% of the measurements by MPR-CT, 87.5% of the measurements by Scanora, and 47.9% of the measurements by OP-100, and the accuracy of the 4 methods ranked in the order of Direct-CT, MPR-CT, Scanora, and OP-100. A similar tendency was observed in the measurements of other anatomic structures, and statistically significant differences were observed among the methods. Thus, MPR-CT allows more accurate measurements than by the other 2 tomographic techniques,and to be useful as a preoperative examination for implant surgery. Résumé Cette étude a été menée afin de comparer la précision de la détermination du contour de la mandibule et de la position du canal mandibulaire dans des mandiblules de cadavres par la méthode de reconstruction par multi-plans (MPR-CT), qui a récemment été très utilisée pour les examens préopératoires, avec celle des techniques de tomographie et d'évaluer l'utilité de MPR-CT en utilisant trois systèmes d'image; c.-à-d. le scanner CT Quantum, le Scanora et l'OP-100, Six sites ont été balayés dans la région molaire de trois mandibules de cadavres. Les images obtenues ont été mesurées deux fois par quatre radiologues. Les structures anatomiques mesurées étaient la hauteur et l'épaisseur de la mandibule, la distance du rebord alvéolaire jusqu'au canal mandibulaire et la distance de l'os cortical vestibulaire au canal mandibulaire. Après balayage, les zones balayées des mandibules ont été coupées en tranches d'une épaisseur de 2 mm et des images radiographiques de ces tranches ont été obtenues. Les valeurs des quatre structures anatomiques mentionnées précédemment obtenues par les mesures des radiogrammes utilisant les compas digitaux étaient considérées comme valeurs correctes. Lorsqu'elles étaient comparées aux valeurs correctes, les erreurs dans la distance du rebord alvéolaire jusqu'au canal mandibulaire étaient inférieures à 1±1 mm dans 94 % des mesures par CT-Direct, 90% dans les mesures par MPR-CT, 88% des mesures par Scanora et 48% des mesures par OP-100, et la précision des quatre méthodes était dans l'ordre CT-Direct, MPR-CT, Scanora et OP-100. Une tendance semblable a été observée dans les mesures d'autres structures anatomiques et des différences statistiquement significatives ont été observées parmi les méthodes. Le CT-PMR apporte donc plus de mesures précises que les deux autres techniques de tomographie et devrait être utilisé pourl'examen préopératoire lors de la chirurgie implantaire. Zusammenfassung Radiologische Messungen im Unterkiefer: Ein Vergleich zwischen reformatierten CTs und konventionellen tomographischen Bildern Diese Studie wurde durchgeführt, um die Genauigkeit bei der Bestimmung der Kontur des Unterkiefers und bei der Lokalisation des Mandibularkanals in Kadaverunterkiefern durch die multiplanare Rekonstruktionsmethode (MPR-CT) mit konventionellen tomographischen Techniken zu vergleichen. Die MPR-CT wird seit kurzem oft für präoperative Untersuchungen angewendet. Zudem sollte die Anwendbarkeit der MPR-CT untersucht werden. Bei 3 Kadaverunterkiefern wurden je 6 Stellen in der Molarenregion mit 3 verschiedenen Systemen, Quantum CT Scanner, Scanora und OP-100, untersucht. Die erhaltenen Bilder wurden zweimal durch 4 Radiologen ausgewertet. Die folgenden anatomischen Strukturen wurden ausgemessen: Höhe und Dicke des Unterkiefers, Distanz vom Alveolarkamm zum Mandibularkanal und Distanz vom bukkalen kortikalen Knochen zum Mandibularkanal. Nach den Aufnahmen wurden die untersuchten Stellen auf eine Dicke von 2 mm geschnitten und es wurden Röntgenaufnahmen mit weichen Strahlen von den Schnitten angefertigt. Die Werte der obenerwähnten 4 anatomischen Strukturen, welche durch Messungen in den Röntgen mit weicher Strahlung mittels Zirkel mit Digitalanzeige ermittelt worden waren, wurden als wahre Werte angenommen. Im Vergleich zu den wahren Werten lag der Fehler bei der Distanz vom Alveolarkamm zum Mandibularkanal bei 93.7% der Messungen mit direktem CT, bei 89.6% der Messungen mit MPR-CT, bei 87.5% der Messungen mit Scanora und bei 47.9% der Messungen mit dem OP-100 innerhalb von 1mm (±1mm). Die Genauigkeit der 4 Methoden nahm in folgender Reihenfolge ab: direkte CT, MPR-CT, Scanora und OP-100. Eine ähnliche Tendenz konnte bei den Messungen der anderen anatomischen Strukturen beobachtet werden und zwischen den Methoden bestanden statistisch signifikante Unterschiede. Die MPR-CT ergaben genauere Messungen als die zwei anderen tomographischen Techniken. Die Methode ist daher hilfreich bei der präoperativen Untersuchung vor Implantatchirurgie. Resumen Este estudio se llevó a cabo para comparar la exactitud de la determinación del contorno mandibular y la posición del canal mandibular en mandíbulas de cadáver por medio del método de reconstrucción multiplanar (MPR-CT), que recientemente se ha convertido de uso extendido para exámenes preoperatorios, con aquellas técnicas tomográficas y para evaluar la utilidad de MPR-CT. Se escanearon un total de 6 lugares en la región molar de 3 mandíbulas de cadáver usando tres sistemas de imágenes, i.e. escáner Quantum CT, Scanora y OP-100. Las imágenes obtenidas se midieron dos veces cada una por 4 radiólogos. Las estructuras anatómicas medidas fueron altura y grosor de la mandíbula, distancia de la cresta alveolar al canal mandibular, y distancia desde el hueso cortical vestibular al canal mandibular. Tras realizar el escáner, las áreas escaneadas de las mandíbulas se cortaron en lonchas de 2 mm de grosor, y se obtuvieron imágenes radiológicas blandas de estos cortes. Los valores de las ya mencionadas 4 estructuras anatómicas obtenidas por mediciones en los radiogramas radiográficos usando calibres de visualización digital se consideraron como valores reales, los errores en la distancia desde la cresta alveolar al canal mandibular estaban dentro de 1 mm (±1 mm) en 93.7% de las mediciones por CT-directa, 89.6% de las mediciones por MPR_CT, 87.5% de las mediciones por Scanora, y el 47.9% de las mediciones por OP-100, y la exactitud de los 4 métodos se clasificaron en orden de CT-directa, MPR-CT, MPR-CT, Scanora, y OP-100. Se observó una tendencia similar en las mediciones de otras estructuras anatómicas, y se observaron diferencias estadísticamente significativas entre los métodos. De este modo, MPR-CT permite unas mediciones mas exactas que las de las otras 2 técnicas tomográficas, y ser útil como examen preoperatorio para cirugía de implantes. [source]

Identification and inheritance of a partially dominant gene for yellow seed colour in Brassica napus

PLANT BREEDING, Issue 1 2005
X. P. Liu
Abstract A yellow-seeded doubled haploid (DH) line no. 2127-17, derived from a resynthesized Brassica napus L., was crossed with two black-seeded Brassica cultivars ,Quantum' and ,Sprint' of spring type. The inheritance of seed colour was investigated in the F2, and BC1 populations of the two crosses and also in the DH population derived from the F1 of the cross ,Quantum'× no. 2127-17. Seed colour analysis was performed with the colorimeter CR-300 (Minolta, Japan) together with a visual classification system. The immediate F1 seeds of the reciprocals in the two crosses had the same colour as the self-pollinated seeds of the respective black- and yellow-seeded female parents, indicating the maternal control of seed colour. The F1 plants produced yellow-brown seeds that were darker in colour than the seeds of no. 2127-17, indicating the partial dominance of yellow seed over black. In the segregating BC1 progenies of the two crosses, the frequencies of the black- and yellow-seeded plants fit well with a 1 : 1 ratio. In the cross with ,Quantum', the frequencies of yellow-seeded and black-seeded plants fit with a 13 : 3 ratio in the F2 progeny, and with a 3 : 1 ratio in the DH progeny. However, a 49 : 15 segregation ratio was observed for the yellow-seeded and black-seeded plants in the F2 progeny of the cross with ,Sprint'. It was postulated from these results that seed colour was controlled by three pairs of genes. A dominant yellow-seeded gene (Y) was identified in no. 2127-17 that had epistatic effects on the two independent dominant black-seeded genes (B and C), thereby inhibiting the biosynthesis of seed coat pigments. [source]

A Polymorphic Dynamic Network Loading Model

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 2 2008
Nie Yu (Marco)
The polymorphism, realized through a general node-link interface and proper discretization, offers several prominent advantages. First of all, PDNL allows road facilities in the same network to be represented by different traffic flow models based on the tradeoff of efficiency and realism and/or the characteristics of the targeted problem. Second, new macroscopic link/node models can be easily plugged into the framework and compared against existing ones. Third, PDNL decouples links and nodes in network loading, and thus opens the door to parallel computing. Finally, PDNL keeps track of individual vehicular quanta of arbitrary size, which makes it possible to replicate analytical loading results as closely as desired. PDNL, thus, offers an ideal platform for studying both analytical dynamic traffic assignment problems of different kinds and macroscopic traffic simulation. [source]

Photoheterotrophy and light-dependent uptake of organic and organic nitrogenous compounds by Planktothrix rubescens under low irradiance

FRESHWATER BIOLOGY, Issue 10 2003
Tatiana Zotina
Summary 1. Planktothrix rubescens is the dominant photoautotrophic organism in Lake Zürich, a prealpine, deep, mesotrophic freshwater lake with an oxic hypolimnion. Over long periods of the year, P. rubescens accumulates at the metalimnion and growth occurs in situ at irradiance near the photosynthesis compensation point. Experiments were conducted to evaluate the contribution of photoheterotrophy, heterotrophy and light-dependent uptake of nitrogenous organic compounds to the carbon and nitrogen budget of this cyanobacterium under conditions of restricted availability of light quanta. 2. We used both purified natural populations of P. rubescens from the depth of 9 m and an axenic culture grown under low irradiance at 11 ,mol m,2 s,1 on a light : dark cycle (10 : 14 h) to determine the uptake rates of various amino acids, urea, glucose, fructose, acetate and inorganic carbon. The components were added to artificial lake water in low amounts that simulated the naturally occurring potential concentrations. 3. The uptake rates of acetate and amino acids (glycine, serine, glutamate and aspartate) were strongly enhanced at low irradiance as compared with the dark. However, no difference was observed in the uptake of arginine, which was taken up at high rates under both treatments. The uptake rates of glucose, fructose and urea were very low under all conditions. Similar results were obtained for both axenic P. rubescens and for purified natural populations of P. rubescens that were separated from bacterioplankton and other phytoplankton. 4. Metalimnetic P. rubescens that was stratified at low irradiance for weeks exhibited much higher uptake rates than filaments that were entrained in the deepening surface mixed layer and experienced higher irradiance. The added organic compounds contributed up to 62% to the total carbon uptake of metalimnetic P. rubescens. On the basis of a molar C : N ratio of 4.9, the nitrogen uptake as organic compounds satisfied up to 84% of the nitrogen demand. 5. The experiments indicate that photoheterotrophy and light-dependent uptake of nitrogenous organic compounds may contribute significantly to the carbon and nitrogen budget of filaments at low irradiance typical for growth of P. rubescens in the metalimnion and at the bottom of the surface mixed layer. [source]

Organic-walled dinoflagellate cyst production in relation to upwelling intensity and lithogenic influx in the Cape Blanc region (off north-west Africa)

PHYCOLOGICAL RESEARCH, Issue 2 2005
Ewa Susek
SUMMARY Fossil dinoflagellate cyst assemblages are increasingly used in paleoclimatic research to establish paleoenvi-ronmental reconstructions. To obtain reliable reconstructions, it is essential to know which physical factors influence the cyst production. Most information about the relationship between variations in physical parameters and cyst production is known from middle and higher latitudes. Information from the (sub)tropics is rare. To increase this information, the temporal variation in cyst assemblages from the upwelling area off north-west Africa (off Mauritania) has been compared to environmental conditions of the upper water column. Samples were collected by the sediment trap CB9, off north-west Africa (Cape Blanc, 21°15,2,N, 20°42,2,W) between 11 June 1998 and 7 November 1999 at 27.5-day intervals. Off Cape Blanc, upwelling occurs throughout the year with variable intensity. This region is also characterized by frequently occurring Saharan dust storms. Seasonal variations in dust input, upwelling intensity and sea surface temperature are reflected by the production of organic-walled dinoflagellate cyst assemblages. Several cyst taxa are produced throughout the sampling interval, with the highest fluxes at times of strongest upwelling relaxation and/or dust input (Echinidinium aculeatum Zonneveld, Echini-din ium delicatum Zonneveld, Echinidinium granulaturn Zonneveld, Echinidinium spp., Impagidinium aculeatum (Wall) Lentin et Williams, Impagidinium sphaeri-cum (Wall) Lentin et Williams, Protoperidinium americanum (Gran et Braarud) Balech, Protoperidinium stellatum (Wall in Wall et Dale) Rochon etal., Protoperidinium spp., Selenopemphix nephroides (Benedek) Benedek et Sarjeant and Selenopemphix quanta (Bradford) Matsuoka). Species such as, for example, Bitectatodinium spongium (Zonneveld) Zonneveld et Jurkschat and Impagidinium patulum (Wall) Stover et Evitt do not show any production pattern related to a particular season of the year or to specific environmental conditions in the upper water column. The production of cysts of Protoperidinium monospinum (Paulsen) Zonneveld et Dale is restricted to intervals with increased nutrient concentrations in upper waters when sea surface temperatures at the sampling site is below approximately 24°C. [source]

Measurement of gradients of absorbed light in spinach leaves from chlorophyll fluorescence profiles

PLANT CELL & ENVIRONMENT, Issue 12 2000
T. C. Vogelmann
ABSTRACT Profiles of chlorophyll fluorescence were measured in spinach leaves irradiated with monochromatic light. The characteristics of the profiles within the mesophyll were determined by the optical properties of the leaf tissue and the spectral quality of the actinic light. When leaves were infiltrated with 10,4M DCMU [3-(3,4-dichlorophenyl)-1, 1-dimethyl-urea] or water, treatments that minimized light scattering, irradiation with 2000 ,mol m,2 s,1 green light produced broad Gaussian-shaped fluorescence profiles that spanned most of the mesophyll. Profiles for chlorophyll fluorescence in the red (680 ± 16 nm) and far red (, > 710 nm) were similar except that there was elevated red fluorescence near the adaxial leaf surface relative to far red fluorescence. Fluorescence profiles were narrower in non-infiltrated leaf samples where light scattering increased the light gradient. The fluorescence profile was broader when the leaf was irradiated on its adaxial versus abaxial surface due to the contrasting optical properties of the palisade and spongy mesophyll. Irradiation with blue, red and green monochromatic light produced profiles that peaked 50, 100 and 150 ,m, respectively, beneath the irradiated surface. These results are consistent with previous measurements of the light gradient in spinach and they agree qualitatively with measurements of carbon fixation under monochromatic blue, red and green light. These results suggest that chlorophyll fluorescence profiles may be used to estimate the distribution of quanta that are absorbed within the leaf for photosynthesis. [source]

Einstein Lecture , One hundred years of light quanta,

ANNALEN DER PHYSIK, Issue 1 2007
R.J. Glauber
First page of article [source]

The distinction of integer and fractional Quantum Hall Effect is a mathematical artifact without physical merit

ANNALEN DER PHYSIK, Issue 5 2003
E.J. Post
Abstract Many body wave function assessments of the quantum Hall effect are compared with a global assessment using Aharonov-Bohm and Gauss-Ampère period-integrals as counters of flux and charge quanta. Experiment pleads in favor of a two quanta unified description in terms of flux and charge numbers. [source]

Photoelectron Generation by Photosystem,II Core Complexes Tethered to Gold Surfaces

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 4 2010
Michele Vittadello, Prof.
Abstract By using a nondestructive, ultrasensitive, fluorescence kinetic technique, we measure in,situ the photochemical energy conversion efficiency and electron transfer kinetics on the acceptor side of histidine-tagged photosystem,II core complexes tethered to gold surfaces. Atomic force microscopy images coupled with Rutherford backscattering spectroscopy measurements further allow us to assess the quality, number of layers, and surface density of the reaction center films. Based on these measurements, we calculate that the theoretical photoelectronic current density available for an ideal monolayer of core complexes is 43,,A,cm,2 at a photon flux density of 2000,,mol,quanta,m,2,s,1 between 365 and 750,nm. While this current density is approximately two orders of magnitude lower than the best organic photovoltaic cells (for an equivalent area), it provides an indication for future improvement strategies. The efficiency could be improved by increasing the optical cross section, by tuning the electron transfer physics between the core complexes and the metal surface, and by developing a multilayer structure, thereby making biomimetic photoelectron devices for hydrogen generation and chemical sensing more viable. [source]

Improving glycaemic control in children and adolescents: which aspects of therapy really matter?

DIABETIC MEDICINE, Issue 4 2010
T. C. Skinner
Diabet. Med. 27, 369,375 (2010) Abstract In paediatric diabetes, the concept of intensive therapy in the post-Diabetes Control and Complications Trial period has become subverted by a pharmaco-technological paradigm at the expense of other aspects of care such as goal-setting and psychosocial support. This review examines which patients benefit most from intensive therapy in terms of glycaemic control (HbA1c). It also reviews published controlled trial and observational data relating to the impact of various insulin types and delivery systems on glycaemic control and canvasses the literature dealing with the impact of patient support, philosophy of care, goal setting and treating team dynamic on HbA1c. Taking into account the characteristics of those patients who benefit most from intensive therapy, the quantum of HbA1c change and the persistence of changes that have been reported in selected and non-selected patient groups, it appears that there is a clear hierarchy in aspects of therapy that improve glycaemic control for children and adolescents with Type 1 diabetes. Prime issues appear to be patient support, team cohesion and goal setting. The reported glycaemic benefits achieved by an isolated emphasis upon a pharmaco-technological paradigm are limited in children and adolescents. It appears that only after the prime issues have been first considered will the potential benefits of the insulin types and regimens then be realized. [source]

Cover Picture: Fortschritte der Physik 11,12 / 2009

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 11-12 2009
Article first published online: 9 NOV 200
The cover page of 2009 shows high-resolution interference "quantum carpet" patterns for the momentum wave function of an interacting Bose-Einstein condensate (BEC). As time progresses (from back to front), the many-body mean field interaction of the BEC first leads to a broadening of the wave function, but then also to a time-varying interference structure by inducing site-dependent nonlinear phase shifts when the BEC is confined in a spatially periodic potential. Imaging the wave function in momentum space for different times leads to a pattern that one reminds of a carefully woven carpet and is hence termed "quantum carpet". Quantum carpets beautifully demonstrate the surprisingly high matter wave coherence of particle-particle interactions in the zero-temperature limit. [source]

Cover Picture: Fortschritte der Physik 10 / 2009

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 10 2009
Article first published online: 14 SEP 200
The cover page of 2009 shows high-resolution interference "quantum carpet" patterns for the momentum wave function of an interacting Bose-Einstein condensate (BEC). As time progresses (from back to front), the many-body mean field interaction of the BEC first leads to a broadening of the wave function, but then also to a time-varying interference structure by inducing site-dependent nonlinear phase shifts when the BEC is confined in a spatially periodic potential. Imaging the wave function in momentum space for different times leads to a pattern that one reminds of a carefully woven carpet and is hence termed "quantum carpet". Quantum carpets beautifully demonstrate the surprisingly high matter wave coherence of particle-particle interactions in the zero-temperature limit. [source]

Cover Picture: Fortschritte der Physik 9 / 2009

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 9 2009
Article first published online: 21 AUG 200
The cover page of 2009 shows high-resolution interference "quantum carpet" patterns for the momentum wave function of an interacting Bose-Einstein condensate (BEC). As time progresses (from back to front), the many-body mean field interaction of the BEC first leads to a broadening of the wave function, but then also to a time-varying interference structure by inducing site-dependent nonlinear phase shifts when the BEC is confined in a spatially periodic potential. Imaging the wave function in momentum space for different times leads to a pattern that one reminds of a carefully woven carpet and is hence termed "quantum carpet". Quantum carpets beautifully demonstrate the surprisingly high matter wave coherence of particle-particle interactions in the zero-temperature limit. [source]

Cover Picture: Fortschritte der Physik 5,7 / 2009

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 5-7 2009
Article first published online: 27 MAY 200
The cover page of 2009 shows high-resolution interference "quantum carpet" patterns for the momentum wave function of an interacting Bose-Einstein condensate (BEC). As time progresses (from back to front), the many-body mean field interaction of the BEC first leads to a broadening of the wave function, but then also to a time-varying interference structure by inducing site-dependent nonlinear phase shifts when the BEC is confined in a spatially periodic potential. Imaging the wave function in momentum space for different times leads to a pattern that one reminds of a carefully woven carpet and is hence termed "quantum carpet". Quantum carpets beautifully demonstrate the surprisingly high matter wave coherence of particle-particle interactions in the zero-temperature limit. [source]

Cover Picture: Fortschritte der Physik 3,4 /2009

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 3-4 2009
Article first published online: 23 MAR 200
The cover page of 2009 shows high-resolution interference "quantum carpet" patterns for the momentum wave function of an interacting Bose-Einstein condensate (BEC). As time progresses (from back to front), the many-body mean field interaction of the BEC first leads to a broadening of the wave function, but then also to a time-varying interference structure by inducing site-dependent nonlinear phase shifts when the BEC is confined in a spatially periodic potential. Imaging the wave function in momentum space for different times leads to a pattern that one reminds of a carefully woven carpet and is hence termed "quantum carpet". Quantum carpets beautifully demonstrate the surprisingly high matter wave coherence of particle-particle interactions in the zero-temperature limit. [source]

Cover Picture: Fortschritte der Physik 1,2 /2009

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 1-2 2009
Article first published online: 9 FEB 200
The cover page of 2009 shows high-resolution interference "quantum carpet" patterns for the momentum wave function of an interacting Bose-Einstein condensate (BEC). As time progresses (from back to front), the many-body mean field interaction of the BEC first leads to a broadening of the wave function, but then also to a time-varying interference structure by inducing site-dependent nonlinear phase shifts when the BEC is confined in a spatially periodic potential. Imaging the wave function in momentum space for different times leads to a pattern that one reminds of a carefully woven carpet and is hence termed "quantum carpet". Quantum carpets beautifully demonstrate the surprisingly high matter wave coherence of particle-particle interactions in the zero-temperature limit. [source]

Biological energy requirements as quantitative boundary conditions for life in the subsurface

GEOBIOLOGY, Issue 4 2004
T. M. HOEHLER
ABSTRACT All life requires energy, which must be extracted from the environment. For all known life, free energy must be available at finite minimum levels in order to be usefully harnessed and must be delivered at finite minimum rates in order to support basic biochemical integrity and function. While seldom tested in the high energy light- and oxygen-based metabolisms of the surface biosphere, the magnitude of these requirements , the biological energy quantum (BEQ) and maintenance energy (ME) requirements, respectively , is considerable with respect to the potential metabolisms and energy sources that characterize the deep subsurface realm. As such, they constitute a fundamental constraint on the possible nature, distribution, and activity of microbial life in that environment. Because the energy released in a chemical transformation can be equated to the concentrations of substrates and products, both the BEQ and ME requirements define the minimum substrate concentration and minimum substrate production rate that must be sustained by a given environment for it to be capable of supporting life. The magnitudes of the BEQ and ME requirements are sensitive to a range of environmental parameters that may vary significantly in the subsurface. Temperature exerts a particularly strong control and is among the most important parameters to be considered in evaluating the energetic habitability of subsurface environments. [source]

Efficient and Photostable ZnS-Passivated CdS:Mn Luminescent Nanocrystals,

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2004
H. Yang
Abstract Efficient and photostable ZnS-passivated CdS:Mn (CdS:Mn/ZnS core/shell) nanocrystals were synthesized using reverse micelle chemistry. CdS:Mn/ZnS core/shell nanocrystals exhibited much improved luminescent properties (quantum yield and photostability) over organically (n -dodecanethiol-) capped CdS:Mn nanocrystals. This is the result of effective, robust passivation of CdS surface states by the ZnS shell and consequent suppression of non-radiative recombination transitions. The dependence of photoluminescence (PL) intensity has been observed as a function of UV irradiation time for both organically and inorganically capped CdS:Mn nanocrystals. Whereas organically capped CdS:Mn nanocrystals exhibit a significant reduction of PL intensity, CdS:Mn/ZnS core/shell nanocrystals exhibit an increased PL intensity with UV irradiation. XPS (X-ray photoelectron spectroscopy) studies reveal that UV irradiation of CdS:Mn/ZnS nanocrystals in air atmosphere induces the photo-oxidation of the ZnS shell surface, leading to the formation of ZnSO4. This photo-oxidation product is presumably responsible for the enhanced PL emission, serving as a passivating layer. [source]