1,309 research outputs found
Aspects of Defect Topology in Smectic Liquid Crystals
We study the topology of smectic defects in two and three dimensions. We give
a topological classification of smectic point defects and disclination lines in
three dimensions. In addition we describe the combination rules for smectic
point defects in two and three dimensions, showing how the broken translational
symmetry of the smectic confers a path dependence on the result of defect
addition.Comment: 19 pages, 13 figure
Egyptian Agriculture in the 21st Century
In order to perform a proper, integrated assessment of potential climate change impacts on Egypt it was necessary to accurately identify important and impending issues and problems which are and will be facing the Egyptian agriculture sector into the next century. To this aim, two experts in the fields of Agronomy and Irrigated Agriculture in the Middle East were asked to travel to Egypt in order to assess the current state of Egyptian agriculture and pose possible questions and scenarios that will face Egypt in light of its current agricultural practices and management strategies. The paper examines two possible future scenarios for Egypt, one from a non-climate change perspective and the other from a climate change outlook. These scenarios are derived from the authors perspective of the current state of Egyptian agriculture. One viewpoint is that of the pessimist, where Egypt continues to practice poor agriculture management; the other is that of the optimist, with Egypt adopting sound management practices - adapting its cropping pattern and water use practices. Also addressed are the potential impacts of climate change on crop yields and recommendations for agronomic research to mitigate its potential impact
A Chebychev propagator with iterative time ordering for explicitly time-dependent Hamiltonians
A propagation method for time-dependent Schr\"odinger equations with an
explicitly time-dependent Hamiltonian is developed where time ordering is
achieved iteratively. The explicit time-dependence of the time-dependent
Schr\"odinger equation is rewritten as an inhomogeneous term. At each step of
the iteration, the resulting inhomogeneous Schr\"odinger equation is solved
with the Chebychev propagation scheme presented in J. Chem. Phys. 130, 124108
(2009). The iteratively time-ordering Chebychev propagator is shown to be
robust, efficient and accurate and compares very favorably to all other
available propagation schemes
Stable Fermion Bag Solitons in the Massive Gross-Neveu Model: Inverse Scattering Analysis
Formation of fermion bag solitons is an important paradigm in the theory of
hadron structure. We study this phenomenon non-perturbatively in the 1+1
dimensional Massive Gross-Neveu model, in the large limit. We find,
applying inverse scattering techniques, that the extremal static bag
configurations are reflectionless, as in the massless Gross-Neveu model. This
adds to existing results of variational calculations, which used reflectionless
bag profiles as trial configurations. Only reflectionless trial configurations
which support a single pair of charge-conjugate bound states of the associated
Dirac equation were used in those calculations, whereas the results in the
present paper hold for bag configurations which support an arbitrary number of
such pairs. We compute the masses of these multi-bound state solitons, and
prove that only bag configurations which bear a single pair of bound states are
stable. Each one of these configurations gives rise to an O(2N) antisymmetric
tensor multiplet of soliton states, as in the massless Gross-Neveu model.Comment: 10 pages, revtex, no figures; v2: typos corrected, references added;
v3: version accepted for publication in the PRD. referencess added. Some
minor clarifications added at the beginning of section
Prescription-induced jump distributions in multiplicative Poisson processes
Generalized Langevin equations (GLE) with multiplicative white Poisson noise
pose the usual prescription dilemma leading to different evolution equations
(master equations) for the probability distribution. Contrary to the case of
multiplicative gaussian white noise, the Stratonovich prescription does not
correspond to the well known mid-point (or any other intermediate)
prescription. By introducing an inertial term in the GLE we show that the Ito
and Stratonovich prescriptions naturally arise depending on two time scales,
the one induced by the inertial term and the other determined by the jump
event. We also show that when the multiplicative noise is linear in the random
variable one prescription can be made equivalent to the other by a suitable
transformation in the jump probability distribution. We apply these results to
a recently proposed stochastic model describing the dynamics of primary soil
salinization, in which the salt mass balance within the soil root zone requires
the analysis of different prescriptions arising from the resulting stochastic
differential equation forced by multiplicative white Poisson noise whose
features are tailored to the characters of the daily precipitation. A method is
finally suggested to infer the most appropriate prescription from the data
Effects of adenotonsillectomy on plasma inflammatory biomarkers in obese children with obstructive sleep apnea: A community-based study.
BackgroundObesity and obstructive sleep apnea syndrome (OSA) are highly prevalent and frequently overlapping conditions in children that lead to systemic inflammation, the latter being implicated in the various end-organ morbidities associated with these conditions.AimTo examine the effects of adenotonsillectomy (T&A) on plasma levels of inflammatory markers in obese children with polysomnographically diagnosed OSA who were prospectively recruited from the community.MethodsObese children prospectively diagnosed with OSA, underwent T&A and a second overnight polysomnogram (PSG) after surgery. Plasma fasting morning samples obtained after each of the two PSGs were assayed for multiple inflammatory and metabolic markers including interleukin (IL)-6, IL-18, plasminogen activator inhibitor-1 (PAI-1), monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinase-9 (MMP-9), adiponectin, apelin C, leptin and osteocrin.ResultsOut of 122 potential candidates, 100 obese children with OSA completed the study with only one-third exhibiting normalization of their PSG after T&A (that is, apnea-hypopnea index (AHI) ≤1/hour total sleep time). However, overall significant decreases in MCP-1, PAI-1, MMP-9, IL-18 and IL-6, and increases in adropin and osteocrin plasma concentrations occurred after T&A. Several of the T&A-responsive biomarkers exhibited excellent sensitivity and moderate specificity to predict residual OSA (that is, AHI⩾5/hTST).ConclusionsA defined subset of systemic inflammatory and metabolic biomarkers is reversibly altered in the context of OSA among community-based obese children, further reinforcing the concept on the interactive pro-inflammatory effects of sleep disorders such as OSA and obesity contributing to downstream end-organ morbidities
UVA II Exposure of Human Skin Results in Decreased Immunization Capacity, Increased Induction of Tolerance and a Unique Pattern of Epidermal Antigen-Presenting Cell Alteration
The risks incurred from increased exposure to UVA II (320-340 nm) ( i.e. during sunscreen use and extended outdoor exposure, tanning parlors) are not well understood. Therefore, we explored the effects of UVA II on skin immune responses in humans. After a single local exposure (4 minimum erythemal dose [MED]) using a xenon arc lamp filtered with a narrow bandpass filter (335 ± 5 nm full width at half maximum), individuals were contact-sensitized with dinitrochlorobenzene (DNCB) through a UVA II exposure site or through normal skin. UVA II induced a marked decrease in the magnitude of skin immune responses ( P < 0.0001). The UVA II group had only 29% successful sensitizations, as compared to 83% in the control group. The percentage of individuals who remained tolerant to DNCB after two sensitizations was 23.6% for the UVA II-exposed group, as compared to 3.8% in the controls ( P = 0.006). UVA II also uniquely altered the type of antigen-presenting cells present in the epidermis. Human leukocyte antigen (HLA)-DR+ cells in control epidermal cell suspensions (C-EC) comprised a single, homogeneous population of Langerhans cells (LC) with the phenotype: CD1a hi DR mid CD11b − CD36 − (1.5 ± 0.3% of EC). UVA II irradiation reduced the number of such LC to 0.6 ± 0.2% of EC. Although cells expressing the macrophage phenotype: CD1a DR hi CD11b+ CD36+ were increased in UVA II skin, relative to C-EC, these comprised only 10.1 ± 6.1% of the DR+ cells, which is less than that after UVB exposure. Also distinct from UVB, a third population was found in UVA II-EC, which exhibited a novel phenotype: CD1a+ DR+ CD36+ CDllb+; these comprised 11.1 ± 6.9% of the DR+ UVA II-EC. In conclusion, despite the above differences in infiltrating DR cells, both UVB and UVA II reduce the skin's ability to support contact sensitization, induce active suppression (tolerance) and induce a reduction in LC.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73639/1/j.1751-1097.1997.tb01903.x.pd
Biocharts: a visual formalism for complex biological systems
We address one of the central issues in devising languages, methods and tools for the modelling and analysis of complex biological systems, that of linking high-level (e.g. intercellular) information with lower-level (e.g. intracellular) information. Adequate ways of dealing with this issue are crucial for understanding biological networks and pathways, which typically contain huge amounts of data that continue to grow as our knowledge and understanding of a system increases. Trying to comprehend such data using the standard methods currently in use is often virtually impossible. We propose a two-tier compound visual language, which we call Biocharts, that is geared towards building fully executable models of biological systems. One of the main goals of our approach is to enable biologists to actively participate in the computational modelling effort, in a natural way. The high-level part of our language is a version of statecharts, which have been shown to be extremely successful in software and systems engineering. The statecharts can be combined with any appropriately well-defined language (preferably a diagrammatic one) for specifying the low-level dynamics of the pathways and networks. We illustrate the language and our general modelling approach using the well-studied process of bacterial chemotaxis
Experimental Evidence for Quantum Structure in Cognition
We proof a theorem that shows that a collection of experimental data of
membership weights of items with respect to a pair of concepts and its
conjunction cannot be modeled within a classical measure theoretic weight
structure in case the experimental data contain the effect called
overextension. Since the effect of overextension, analogue to the well-known
guppy effect for concept combinations, is abundant in all experiments testing
weights of items with respect to pairs of concepts and their conjunctions, our
theorem constitutes a no-go theorem for classical measure structure for common
data of membership weights of items with respect to concepts and their
combinations. We put forward a simple geometric criterion that reveals the non
classicality of the membership weight structure and use experimentally measured
membership weights estimated by subjects in experiments to illustrate our
geometrical criterion. The violation of the classical weight structure is
similar to the violation of the well-known Bell inequalities studied in quantum
mechanics, and hence suggests that the quantum formalism and hence the modeling
by quantum membership weights can accomplish what classical membership weights
cannot do.Comment: 12 pages, 3 figure
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