196,781 research outputs found
Difference points in extractive and reactive cascades. II — Generating design alternatives by the lever rule for reactive systems
No full textUsing linear combinations of vectors in composition space, we formulate a lever rule for reactive distillation columns. This lever rule facilitates the proposal of alternative sequences of reactive distillation systems by allowing us to visualize how material balance constraints move as a Function of reaction "turnover". our approach uses the concept of a pseudo-feed, which is the composition that results from mixing column distillate and bottom products. Our lever rule for reactive distillation columns uses linear combinations of so-called reaction difference points, stoichiometric coefficient vectors of reactants and products, and composition vectors. When a reaction causes no change in the total number of moles, the reaction difference point moves to infinity (Hauan, Omtveit & Lien (1996). Paper 5f, A.I.Ch.E. Annual Meeting, Chicago, Hauan, Westerberg & Lien (1999a). Chemical Engineering Science, 55(6), 1053-1075, Hauan, Ciric, Westerberg & Lien (1999b). Chemical Engineering Science, in press). We show how to carry out all geometric constructions entirely within a finite composition domain by decomposing the total stoichiometric coefficient vector into product and reactant stoichiometric coefficient vectors. In this case the lever rule compares distances along two parallel vectors. For an infinite extractive difference point (Westerberg & Wahnschafft (1996). Advances in Chemical Engineering, 23, 63-170) we can confine all geometric manipulations when proposing alternative reactive distillation processes to a finite composition domain by combining the vectors in a different order. (C) 2000 Elsevier Science Ltd. All rights reserved
Experimental quantum cosmology in time-dependent optical media
No full textIt is possible to construct artificial spacetime geometries for light by using intense laser pulses that modify the spatiotemporal properties of an optical medium. Here we theoretically investigate experimental possibilities for studying spacetime metrics of the form . By tailoring the laser pulse shape and medium properties, it is possible to create a refractive index variation that can be identified with . Starting from a perturbative solution to a generalized Hopfield model for the medium described by an , we provide estimates for the number of photons generated by the time-dependent spacetime. The simplest example is that of a uniformly varying that therefore describes the Robertson–Walker metric, i.e. a cosmological expansion. The number of photon pairs generated in experimentally feasible conditions appears to be extremely small. However, large photon production can be obtained by periodically modulating the medium and thus resorting to a resonant enhancement similar to that observed in the dynamical Casimir effect. Curiously, the spacetime metric in this case closely resembles that of a gravitational wave. Motivated by this analogy, we show that a periodic gravitational wave can indeed act as an amplifier for photons. The emission for an actual gravitational wave will be very weak but should be readily observable in the laboratory analogue
Non-standard interactions using the OPERA experiment
No full textWe investigate the implications of non-standard interactions on neutrino oscillations in the OPERA experiment. In particular, we study the non-standard interaction parameter epsilon(mu tau) . We show that the OPERA experiment has a unique opportunity to reduce the allowed region for this parameter compared with other experiments such as the MINOS experiment, mostly due to the higher neutrino energies in the CNGS beam compared to the NuMI beam. We find that OPERA is mainly sensitive to a combination of standard and non-standard parameters and that a resulting anti-resonance effect could suppress the expected number of events. Furthermore, we show that running OPERA for five years each with neutrinos and anti-neutrinos would help in resolving the degeneracy between the standard parameters and epsilon(mu tau) . This scenario is significantly better than the scenario with a simple doubling of the statistics by running with neutrinos for ten years.QC 2010052
Negative frequency resonant radiation in quadratic media
No full textSolitons emit resonant radiation (RR) owing to a universal mechanism of phase-matching with linear waves ruled by perturbing higher-order dispersive terms. Well-known examples range from fiber [1,2] to Langmuir plasma [3] or water wave solitons. During the last decade, optical fibers offered the unique opportunity to deepen the physics of RR [4], with important applicative fall-out in supercontinuum generation [5], where RR is responsible for broadening the spectrum over the blue-shifted (normally dispersive) region. More recently, the field was significantly advanced by important results recognizing the role of RR in turbulence transport, the observation of RR in different settings encompassing tapered and noble-gas-filled photonic crystal fibers, slow-light waveguides, spatial diffraction in arrays, and second-harmonic generation (SHG). Importantly, it was also shown that, in Kerr media, new frequencies can be generated owing to the coupling with the negative-frequency part of the spectrum, a process termed negative-frequency resonant radiation (NRR) [6]
Working memory : development, disorders and training
No full textWorking memory (WM) is the ability to keep information online during a short period of time. Brain regions underlying WM functioning are found in the frontal and parietal cortices. It is largely unknown to what extent the neural substrates underlying WM are susceptible to training induced change. Here we investigate the development of WM capacity, if improvement by training is possible and explore the neuronal correlates for training induced change.In Study I we used functional magnetic resonance imaging (fMRI) to investigate the neural correlates of the developmental change in WM capacity during childhood. We found that during performance of a visuo-spatial working memory test (VSWM), there was a significantly higher activity in the superior frontal and intraparietal cortex in subjects with higher capacity. Thus, the development of these areas may underlie the development of VSWM during childhood.In Study II we used the VSWM test in children with and without ADHD and found that the test differentiated between these groups (PIn Study III (N=14), we saw significant improvements in the treatment group as compared to the control group on the trained WM task (P In Study IV the effects on the cognitive tests were replicated at a significance level of .01, with a randomized, double-blind, placebo-controlled multi-center design (N=44). In this study we also found generalisation of training effects to the behavioural level as evaluated by parents and teachers (inattention (P In Study V we investigated if stroke patients with significant WM deficits also could benefit from training. Participants suffering stroke one to three years earlier gained significant improvements in WM capacity (digit span p Study VI was undertaken to explore the neuronal correlates of WM improvement. Healthy young adults underwent fMRI before and after WM training. Task specific increases in brain activity were found in prefrontal and parietal cortices. These regions are known to underlie WM functioning.Summary: WM shows a prolonged developmental course in humans. WM deficits are prominent in ADHD and following brain injury. However, WM can be improved by training and the treatment effect also generalizes to other cognitive tasks. The increase in WM capacity during childhood as well as after training is associated with increased brain activity in the prefrontal and parietal cortex.List of scientific papersI. Klingberg T, Forssberg H, Westerberg H (2002). Increased brain activity in frontal and parietal cortex underlies the development of visuospatial working memory capacity during childhood. J Cogn Neurosci. 14(1): 1-10. https://pubmed.ncbi.nlm.nih.gov/11798382II. Westerberg H, Hirvikoski T, Forssberg H, Klingberg T (2004). Visuo-spatial working memory span: a sensitive measure of cognitive deficits in children with ADHD. Child Neuropsychology. [Accepted] III. Klingberg T, Forssberg H, Westerberg H (2002). Training of working memory in children with ADHD. J Clin Exp Neuropsychol. 24(6): 781-91. https://pubmed.ncbi.nlm.nih.gov/12424652IV. Klingberg T, Fernell E, Olesen P, Johnson M, Gustafsson P, Dahlstrom K, Gillberg CG, Forssberg H, Westerberg H (2004). Computerized training of working memory in children with Attention-Deficit/Hyperavtivity Disorder - a controlled, randomized, double-blind, trial. [Submitted] V. Westerberg H, Jacobaeus H, Hirvikoski T, Clevberger P, Ostensson ML, Bartfai A, Klingberg T (2004). Computerized working memory training - a method cognitive rehabilitation after stroke. [Submitted]VI. Olesen PJ, Westerberg H, Klingberg T (2004). Increased prefrontal and parietal activity after training of working memory. Nat Neurosci. 7(1): 75-9. Epub 2003 Dec 14. https://pubmed.ncbi.nlm.nih.gov/14699419</p
Sevuparin strongly reduces hepcidin expression in cells, mice, and healthy human volunteers
No full textHepcidin is an essential regulator of systemic iron availability mediating both iron uptake from the diet and its release from body stores. Abnormally high hepcidin levels resulting from inflammation in chronic diseases cause iron restriction with the onset of anemia. Restoring physiological levels of hepcidin could contribute to ameliorating anemia in these patients. Heparin derivatives are known to suppress hepcidin expression acting on the BMP/SMAD pathway. The novel heparin derivative sevuparin, modified to markedly reduce its anticoagulant activity, is proposed as a promising hepcidin antagonizing strategy. Sevuparin was tested for its anti-hepcidin properties in vitro in HepG2 cells, in vivo in mice, and in healthy volunteers. Sevuparin strongly suppressed basal, BMP6-, and IL6-dependent hepcidin expression in HepG2 cells in a dose- and time-dependent manner, modulating the essential BMP6/SMAD cascade. These effects were evident in C57BL/6J mice after intravenous injection of a single dose of sevuparin (20 mg/kg) with a 70% reduction of hepcidin mRNA. Remarkably, similar effects were observed in healthy volunteers following single subcutaneous doses at 3, 6, and 9 mg/kg with 40%-50% suppression at 3 and 6 mg/kg and 72% at 9 mg/kg. Moreover, sevuparin was able to reduce hepcidin upregulation in a mouse model of acute inflammation induced by LPS, also showing an amelioration of the inflammatory markers. Combined with its excellent safety profile, these data suggest a role for sevuparin in treating high-hepcidin disorders
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Non-extremal fractional branes
No full textWe construct non-extremal fractional D-brane solutions of type-II string theory at the Z_2 orbifold point of K3. These solutions generalize known extremal fractional-brane solutions and provide further insights into N=2 supersymmetric gauge theories and dual descriptions thereof. In particular, we find that for these solutions the horizon radius cannot exceed the non-extremal enhancon radius. As a consequence, we conclude that a system of non-extremal fractional branes cannot develop into a black brane. This conclusion is in agreement with known dual descriptions of the system.We construct non-extremal fractional D-brane solutions of type-II string theory at the Z_2 orbifold point of K3. These solutions generalize known extremal fractional-brane solutions and provide further insights into N=2 supersymmetric gauge theories and dual descriptions thereof. In particular, we find that for these solutions the horizon radius cannot exceed the non-extremal enhancon radius. As a consequence, we conclude that a system of non-extremal fractional branes cannot develop into a black brane. This conclusion is in agreement with known dual descriptions of the system.We construct non-extremal fractional D-brane solutions of type-II string theory at the Z_2 orbifold point of K3. These solutions generalize known extremal fractional-brane solutions and provide further insights into N=2 supersymmetric gauge theories and dual descriptions thereof. In particular, we find that for these solutions the horizon radius cannot exceed the non-extremal enhancon radius. As a consequence, we conclude that a system of non-extremal fractional branes cannot develop into a black brane. This conclusion is in agreement with known dual descriptions of the system.We construct non-extremal fractional D-brane solutions of type-II string theory at the Z_2 orbifold point of K3. These solutions generalize known extremal fractional-brane solutions and provide further insights into N=2 supersymmetric gauge theories and dual descriptions thereof. In particular, we find that for these solutions the horizon radius cannot exceed the non-extremal enhancon radius. As a consequence, we conclude that a system of non-extremal fractional branes cannot develop into a black brane. This conclusion is in agreement with known dual descriptions of the system.We construct non-extremal fractional D-brane solutions of type-II string theory at the Z 2 orbifold point of K3. These solutions generalize known extremal fractional-brane solutions and provide further insights into N =2 supersymmetric gauge theories and dual descriptions thereof. In particular, we find that for these solutions the horizon radius cannot exceed the non-extremal enhançon radius. As a consequence, we conclude that a system of non-extremal fractional branes cannot develop into a black brane. This conclusion is in agreement with known dual descriptions of the system
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