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Energy Deposition (energy + deposition)
Selected AbstractsIntense heavy ion beams as a tool to induce high-energy-density states in matterCONTRIBUTIONS TO PLASMA PHYSICS, Issue 5-6 2003N.A. Tahir Abstract Because of the volume character of energy deposition of energetic ions in matter, an intense heavy ion beam is a very suitable laboratory tool to create large samples of high-energy-density matter. This paper shows with the help of two-dimensional numerical simulations how such an intense heavy ion beam can be employed to achieve this goal. The beam parameters considered in this study are those of the beams that are delivered by the existing heavy ion synchrotron, SIS18 and that which will be available at the future facility SIS100, respectively at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fast-spin-echo imaging of inner fields-of-view with 2D-selective RF excitationsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2010Jürgen Finsterbusch PhD Abstract Purpose: To demonstrate the feasibility of two-dimensional selective radio frequency (2DRF) excitations for fast-spin-echo imaging of inner fields-of-view (FOVs) in order to shorten acquisitions times, decrease RF energy deposition, and reduce image blurring. Materials and Methods: Fast-spin-echo images (in-plane resolution 1.0 × 1.0 mm2 or 0.5 × 1.0 mm2) of inner FOVs (40 mm, 16 mm oversampling) were obtained in phantoms and healthy volunteers on a 3 T whole-body MR system using blipped-planar 2DRF excitations. Results: Positioning the unwanted side excitations in the blind spot between the image section and the slice stack to measure yields minimum 2DRF pulse durations (about 6 msec) that are compatible with typical echo spacings of fast-spin-echo acquisitions. For the inner FOVs, the number of echoes and refocusing RF pulses is considerably reduced which compared to a full FOV (182 mm) reduces the RF energy deposition by about a factor of three and shortens the acquisition time, e.g., from 39 seconds to 12 seconds for a turbo factor of 15 or from 900 msec to 280 msec for a single-shot acquisition, respectively. Furthermore, image blurring occurring for high turbo factors as in single-shot acquisitions is considerably reduced yielding effectively higher in-plane resolutions. Conclusion: Inner-FOV acquisitions using 2DRF excitations may help to shorten acquisitions times, ameliorate image blurring, and reduce specific absorption rate (SAR) limitations of fast-spin-echo (FSE) imaging, in particular at higher static magnetic fields. J. Magn. Reson. Imaging 2010;31:1530,1537. © 2010 Wiley-Liss, Inc. [source] SAR and power implications of different RF shimming strategies in the pelvis for 7T MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2009Bob van den Bergen MSc Abstract Purpose To determine the best radiofrequency (RF) shimming method for 7 T body imaging that provides sufficient B1+ excitation inside the target region while energy deposition (SAR) and power demands are as low as possible and that does not incorporate anatomy specific electric field information inside the patient models, as this information is not available in practice. Materials and Methods Finite difference time domain (FDTD) simulations were used to evaluate five RF shimming strategies for the pelvis inside a body coil. The results were compared to the theoretical best solution that could be achieved if the electric field inside the patient was known. Results Most of the RF shimming strategies were successful. However, between the different strategies a factor of two difference in average SAR reduction, a factor of three difference in local maximum SAR reduction, and a factor of 20 difference in power efficiency was observed. Phase matching was found to be the most promising RF shimming method for the body coil used and patient models. Conclusion RF shimming can reduce the SAR and improve power efficiency in an accurate patient model without knowing the electric field. However, choosing the right method is critical to prevent unexpected behavior in local SAR deposition. J. Magn. Reson. Imaging 2009;30:194,202. © 2009 Wiley-Liss, Inc. [source] Determination of X-ray flux using silicon pin diodesJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2009Robin L. Owen Accurate measurement of photon flux from an X-ray source, a parameter required to calculate the dose absorbed by the sample, is not yet routinely available at macromolecular crystallography beamlines. The development of a model for determining the photon flux incident on pin diodes is described here, and has been tested on the macromolecular crystallography beamlines at both the Swiss Light Source, Villigen, Switzerland, and the Advanced Light Source, Berkeley, USA, at energies between 4 and 18,keV. These experiments have shown that a simple model based on energy deposition in silicon is sufficient for determining the flux incident on high-quality silicon pin diodes. The derivation and validation of this model is presented, and a web-based tool for the use of the macromolecular crystallography and wider synchrotron community is introduced. [source] Pulpal effects of enamel ablation with a microsecond pulsed ,,=,9.3-µm CO2 laserLASERS IN SURGERY AND MEDICINE, Issue 4 2009Michal Staninec DDS Abstract Background and Objectives In vitro studies have shown that CO2 lasers operating at the highly absorbed 9.3 and 9.6-µm wavelengths with a pulse duration in the range of 10,20-microsecond are well suited for the efficient ablation of enamel and dentin with minimal peripheral thermal damage. Even though these CO2 lasers are highly promising, they have yet to receive FDA approval. Clinical studies are necessary to determine if excessive heat deposition in the tooth may have any detrimental pulpal effects, particularly at higher ablative fluencies. The purpose of this study was to evaluate the pulpal safety of laser irradiation of tooth occlusal surfaces under the conditions required for small conservative preparations confined to enamel. Study Design/Materials and Methods Test subjects requiring removal of third molar teeth were recruited and teeth scheduled for extraction were irradiated using a pulsed CO2 laser at a wavelength of 9.3 µm operating at 25 or 50 Hz using a incident fluence of 20 J/cm2 for a total of 3,000 laser pulses (36 J) for both rates with water cooling. Two control groups were used, one with no treatment and one with a small cut made with a conventional high-speed hand-piece. No anesthetic was used for any of the procedures and tooth vitality was evaluated prior to treatment by heat, cold and electrical testing. Short term effects were observed on teeth extracted within 72 hours after treatment and long term effects were observed on teeth extracted 90 days after treatment. The pulps of the teeth were fixed with formalin immediately after extraction and subjected to histological examination. Additionally, micro-thermocouple measurements were used to estimate the potential temperature rise in the pulp chamber of extracted teeth employing the same irradiation conditions used in vivo. Results Pulpal thermocouple measurements showed the internal temperature rise in the tooth was within safe limits, 3.3±1.4°C without water cooling versus 1.7±1.6°C with water-cooling, n,=,25, P<0.05. None of the control or treatment groups showed any deleterious effects on pulpal tissues and none of the 29 test-subjects felt pain or discomfort after the procedure. Only two test-subjects felt discomfort from "cold sensitivity" during the procedure caused by the water-spray. Conclusion It appears that this CO2 laser can ablate enamel safely without harming the pulp under the rate of energy deposition employed in this study. Lasers Surg. Med. 41:256,263, 2009. © 2009 Wiley-Liss, Inc. [source] Rapid 3D-T1, mapping of the knee joint at 3.0T with parallel imagingMAGNETIC RESONANCE IN MEDICINE, Issue 3 2006S. Kubilay Pakin Abstract Three-dimensional spin-lattice relaxation time in the rotating frame (3D-T1,) with parallel imaging at 3.0T was implemented on a whole-body clinical scanner. A 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster was combined with generalized autocalibrating partially parallel acquisitions (GRAPPA) to acquire T1, -weighted images. 3D-T1, maps of an agarose phantom and three healthy subjects were constructed using an eight-channel phased-array coil without parallel imaging and with parallel imaging acceleration factors of 2 and 3, in order to assess the reproducibility of the method. The coefficient of variation (CV) of the median T1, of the agarose phantom was 0.44%, which shows excellent reproducibility. The reproducibility of in vivo 3D-T1, maps was also investigated in three healthy subjects. The CV of the median T1, of the patellar cartilage varied between ,1.1% and 4.3%. Similarly, the CV varied between ,2.1,5.8%, ,1.4,8.7%, and ,1.5,4.1% for the biceps femoris and lateral and medial gastrocnemius muscles, respectively. The preliminary results demonstrate that 3D-T1, maps can be constructed with good reproducibility using parallel imaging. 3D-T1, with parallel imaging capability is an important clinical tool for reducing both the total acquisition time and RF energy deposition at 3T. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Activation of large lons in FT-ICR mass spectrometryMASS SPECTROMETRY REVIEWS, Issue 2 2005Julia Laskin Abstract The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has enabled the extension of mass spectrometric methods to large molecules and molecular complexes. This both greatly extends the applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of these applications. This review emphasizes the most promising methods for activation and dissociation of complex ions and presents this discussion in the context of general knowledge of reaction kinetics and dynamics largely established for small ions. We then introduce the characteristic differences associated with the higher number of internal degrees of freedom and high density of states associated with molecular complexity. This is reflected primarily in the kinetics of unimolecular dissociation of complex ions, particularly their slow decay and the higher energy content required to induce decomposition,the kinetic shift (KS). The longer trapping time of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) significantly reduces the KS, which presents several advantages over other methods for the investigation of dissociation of complex molecules. After discussing general principles of reaction dynamics related to collisional activation of ions, we describe conventional ways to achieve single- and multiple-collision activation in FT-ICR MS. Sustained off-resonance irradiation (SORI),the simplest and most robust means of introducing the multiple collision activation process,is discussed in greatest detail. Details of implementation of this technique, required control of experimental parameters, limitations, and examples of very successful application of SORI-CID are described. The advantages of high mass resolving power and the ability to carry out several stages of mass selection and activation intrinsic to FT-ICR MS are demonstrated in several examples. Photodissociation of ions from small molecules can be effected using IR or UV/vis lasers and generally requires tuning lasers to specific wavelengths and/or utilizing high flux, multiphoton excitation to match energy levels in the ion. Photodissociation of complex ions is much easier to accomplish from the basic physics perspective. The quasi-continuum of vibrational states at room temperature makes it very easy to pump relatively large amounts of energy into complex ions and infrared multiphoton dissociation (IRMPD) is a powerful technique for characterizing large ions, particularly biologically relevant molecules. Since both SORI-CID and IRMPD are slow activation methods they have many common characteristics. They are also distinctly different because SORI-CID is intrinsically selective (only ions that have a cyclotron frequency close to the frequency of the excitation field are excited), whereas IRMPD is not (all ions that reside on the optical path of the laser are excited). There are advantages and disadvantages to each technique and in many applications they complement each other. In contrast with these slow activation methods, the less widely appreciated activation method of surface induced dissociation (SID) appears to offer unique advantages because excitation in SID occurs on a sub-picosecond time scale, instantaneously relative to the observation time of any mass spectrometer. Internal energy deposition is quite efficient and readily adjusted by altering the kinetic energy of the impacting ion. The shattering transition,instantaneous decomposition of the ion on the surface,observed at high collision energies enables access to dissociation channels that are not accessible using SORI-CID or IRMPD. Finally, we discuss some approaches for tailoring the surface to achieve particular aims in SID. © 2004 Wiley Periodicals, Inc., Mass Spec Rev 24:135,167, 2005 [source] Maternal Nutrition and Perinatal SurvivalNUTRITION REVIEWS, Issue 10 2001David Rush M.D. The simple relationship between maternal macro-nutrient status and perinatal survival (increased ma-cronutrient intake , increased maternal weight and/or weight gain , increased fetal growth , improved survival) that is usually posited is no longer defensible. First, maternal weight and weight gain are remarkably resistant to either dietary advice or supplementation; further, increased birth weight attributable to maternal nutrition does not necessarily increase perinatal survival (because prepregnant weight is positively associated with both birth weight and higher perinatal mortality). Finally, whereas dietary supplements during pregnancy may have a modest effect on birth weight in nonfamine conditions (by contrast with a large effect in famine or near-famine conditions), their impact is not mediated by maternal energy deposition. Rather, the component of maternal weight gain associated with accelerated fetal growth is maternal water (presumably plasma) volume. [source] The ,-particle excited scintillation response of YAG:Ce thin films grown by liquid phase epitaxyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009Petr Prusa Abstract Y3Al5O12:Ce (YAG:Ce) thin films were grown from PbO-, BaO-, and MoO3 -based fluxes using the liquid phase epitaxy (LPE) method. Photoelectron yield, its time dependence within 0.5,10 ,s shaping time, and energy resolution of these samples were measured under ,-particle excitation. For comparison a sample of the Czochralski grown bulk YAG:Ce single crystal was measured as well. Photoelectron yield values of samples grown from the BaO-based flux were found superior to other LPE films and comparable with that of the bulk single crystal. The same is valid also for the time dependence of photoelectron yield. Obtained results are discussed taking into account the influence of the flux and technology used. Additionally, , particle energy deposition in very thin films is modelled and discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The energy cascade from warm dark matter decaysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008M. Valdés ABSTRACT We use a set of Monte Carlo simulations to follow the cascade produced by a primary electron of energy Ein in the intergalactic medium. We choose Ein= 3,10 keV as expected from the decay of one of the most popular warm dark matter (WDM) candidates, sterile neutrinos. Our simulation takes into account processes previously neglected such as free,free interactions with ions and recombinations, and uses the best available cross-sections for collisional ionizations and excitations with H and He and for electron,electron collisions. We precisely derive the fraction of the primary electron energy that heats the gas, ionizes atoms and produces line and continuum photons as a function of the ionization fraction. Handy fitting formulae for all the above energy depositions are provided. By keeping track of the individual photons, we can distinguish between photons in the Ly, resonance and those with energy E < 10.2 eV that do not interact further with gas. This separation is important because a Ly, background can heat or cool the gas depending on the nature of the photons, and can have effects on the 21-cm radiation emitted by neutral H, which will probably become detectable at z > 6 in the near future by the next generation radio interferometers. [source] Concerning the instantaneous mass and the extent of an expanding universeASTRONOMISCHE NACHRICHTEN, Issue 7 2006H. J. Fahr Abstract In this article we want to answer the cosmologically relevant question what, with some good semantic and physical reason, could be called the massMu of an infinitely extended, homogeneously matter-filled and expanding universe. To answer this question we produce a space-like sum of instantaneous cosmic energy depositions surrounding equally each spacepoint in the homogeneous universe. We calculate the added-up instantaneous cosmic energy per volume around an arbitrary space point in the expanding universe. To carry out this sum we use as basic metrics an analogy to the inner Schwarzschild metric applied to stars, but this time applied to the spacepoint-related universe. It is then shown that this leads to the added-up proper energy within a sphere of a finite outer critical radius defining the point-related infinity. As a surprise this radius turns out to be reciprocal to the square root of the prevailing average cosmic energy density. The equivalent mass of the universe can then also be calculated and, by the expression which is obtained here, shows a scaling with this critical radius of this universe, a virtue of the universe which was already often called for in earlier works by E. Mach, H. Thirring and F. Hoyle and others. This radius on the other hand can be shown to be nearly equal to the Schwarzschild radius of the so-defined mass Mu of the universe. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||