9,745 research outputs found
Stochastic Aggregation: Scaling Properties
We study scaling properties of stochastic aggregation processes in one
dimension. Numerical simulations for both diffusive and ballistic transport
show that the mass distribution is characterized by two independent nontrivial
exponents corresponding to the survival probability of particles and monomers.
The overall behavior agrees qualitatively with the mean-field theory. This
theory also provides a useful approximation for the decay exponents, as well as
the limiting mass distribution.Comment: 6 pages, 7 figure
Synthesis and Properties of Dipyridylcyclopentenes
A short and general route to the substituted dipyridylcyclopentenes was explored and several new compounds belonging to this new group of diarylethenes were synthesized. The study of their photochromic and thermochromic properties shows that the rate of the thermal ring opening is strongly dependent on the polarity of the solvent.
On high energy tails in inelastic gases
We study the formation of high energy tails in a one-dimensional kinetic
model for granular gases, the so-called Inelastic Maxwell Model. We introduce a
time- discretized version of the stochastic process, and show that continuous
time implies larger fluctuations of the particles energies. This is due to a
statistical relation between the number of inelastic collisions undergone by a
particle and its average energy. This feature is responsible for the high
energy tails in the model, as shown by computer simulations and by analytical
calculations on a linear Lorentz model.Comment: 8 pages, 2 figures, submitted to physica
Supergravity Higgs Inflation and Shift Symmetry in Electroweak Theory
We present a model of inflation in a supergravity framework in the Einstein
frame where the Higgs field of the next to minimal supersymmetric standard
model (NMSSM) plays the role of the inflaton. Previous attempts which assumed
non-minimal coupling to gravity failed due to a tachyonic instability of the
singlet field during inflation. A canonical K\"{a}hler potential with
\textit{minimal coupling} to gravity can resolve the tachyonic instability but
runs into the -problem. We suggest a model which is free of the
-problem due to an additional coupling in the K\"{a}hler potential which
is allowed by the Standard Model gauge group. This induces directions in the
potential which we call K-flat. For a certain value of the new coupling in the
(N)MSSM, the K\"{a}hler potential is special, because it can be associated with
a certain shift symmetry for the Higgs doublets, a generalization of the shift
symmetry for singlets in earlier models. We find that K-flat direction has
This shift symmetry is broken by interactions coming from
the superpotential and gauge fields. This direction fails to produce successful
inflation in the MSSM but produces a viable model in the NMSSM. The model is
specifically interesting in the Peccei-Quinn (PQ) limit of the NMSSM. In this
limit the model can be confirmed or ruled-out not just by cosmic microwave
background observations but also by axion searches.Comment: matches the published version at JCA
Governance and Capacity to Manage Resilience of Health Systems: Towards a New Conceptual Framework.
The term resilience has dominated the discourse among health systems researchers since 2014 and the onset of the Ebola outbreak in West Africa. There is wide consensus that the global community has to help build more resilient health systems. But do we really know what resilience means, and do we all have the same vision of resilience? The present paper presents a new conceptual framework on governance of resilience based on systems thinking and complexity theories. In this paper, we see resilience of a health system as its capacity to absorb, adapt and transform when exposed to a shock such as a pandemic, natural disaster or armed conflict and still retain the same control over its structure and functions
Conical defects in growing sheets
A growing or shrinking disc will adopt a conical shape, its intrinsic
geometry characterized by a surplus angle at the apex. If growth is slow,
the cone will find its equilibrium. Whereas this is trivial if , the
disc can fold into one of a discrete infinite number of states if is
positive. We construct these states in the regime where bending dominates,
determine their energies and how stress is distributed in them. For each state
a critical value of is identified beyond which the cone touches itself.
Before this occurs, all states are stable; the ground state has two-fold
symmetry.Comment: 4 pages, 4 figures, LaTeX, RevTeX style. New version corresponds to
the one published in PR
A model of fasciculation and sorting in mixed populations of axons
We extend a recently proposed model (Chaudhuri et al., EPL 87, 20003 (2009))
aiming to describe the formation of fascicles of axons during neural
development. The growing axons are represented as paths of interacting directed
random walkers in two spatial dimensions. To mimic turnover of axons, whole
paths are removed and new walkers are injected with specified rates. In the
simplest version of the model, we use strongly adhesive short-range inter-axon
interactions that are identical for all pairs of axons. We generalize the model
to adhesive interactions of finite strengths and to multiple types of axons
with type-specific interactions. The dynamic steady state is characterized by
the position-dependent distribution of fascicle sizes. With distance in the
direction of axon growth, the mean fascicle size and emergent time scales grow
monotonically, while the degree of sorting of fascicles by axon type has a
maximum at a finite distance. To understand the emergence of slow time scales,
we develop an analytical framework to analyze the interaction between
neighboring fascicles.Comment: 19 pages, 13 figures; version accepted for publication in Phys Rev
Analyzing Recent Coronary Heart Disease Mortality Trends in Tunisia between 1997 and 2009.
BACKGROUND: In Tunisia, Cardiovascular Diseases are the leading causes of death (30%), 70% of those are coronary heart disease (CHD) deaths and population studies have demonstrated that major risk factor levels are increasing.
OBJECTIVE: To explain recent CHD trends in Tunisia between 1997 and 2009.
METHODS: DATA SOURCES: Published and unpublished data were identified by extensive searches, complemented with specifically designed surveys.
ANALYSIS: Data were integrated and analyzed using the previously validated IMPACT CHD policy model. Data items included: (i)number of CHD patients in specific groups (including acute coronary syndromes, congestive heart failure and chronic angina)(ii) uptake of specific medical and surgical treatments, and(iii) population trends in major cardiovascular risk factors (smoking, total cholesterol, systolic blood pressure (SBP), body mass index (BMI), diabetes and physical inactivity).
RESULTS: CHD mortality rates increased by 11.8% for men and 23.8% for women, resulting in 680 additional CHD deaths in 2009 compared with the 1997 baseline, after adjusting for population change. Almost all (98%) of this rise was explained by risk factor increases, though men and women differed. A large rise in total cholesterol level in men (0.73 mmol/L) generated 440 additional deaths. In women, a fall (-0.43 mmol/L), apparently avoided about 95 deaths. For SBP a rise in men (4 mmHg) generated 270 additional deaths. In women, a 2 mmHg fall avoided 65 deaths. BMI and diabetes increased substantially resulting respectively in 105 and 75 additional deaths. Increased treatment uptake prevented about 450 deaths in 2009. The most important contributions came from secondary prevention following Acute Myocardial Infarction (AMI) (95 fewer deaths), initial AMI treatments (90), antihypertensive medications (80) and unstable angina (75).
CONCLUSIONS: Recent trends in CHD mortality mainly reflected increases in major modifiable risk factors, notably SBP and cholesterol, BMI and diabetes. Current prevention strategies are mainly focused on treatments but should become more comprehensive
Chiral Amplification of Phosphoramidates of Amines and Amino Acids in Water
The origin of biomolecular homochirality continues to be one of the most fascinating aspects of prebiotic chemistry. Various amplification strategies for chiral compounds to enhance a small chiral preference have been reported, but none of these involves phosphorylation, one of nature's essential chemical reactions. Here we present a simple and robust concept of phosphorylation-based chiral amplification of amines and amino acids in water. By exploiting the difference in solubility of a racemic phosphoramidate and its enantiopure form, we achieved enantioenrichment in solution. Starting with near racemic, phenylethylamine-based phosphoramidates, ee's of up to 95 % are reached in a single amplification step. Particularly noteworthy is the enantioenrichment of phosphorylated amino acids and their derivatives, which might point to a potential role of phosphorus en-route to prebiotic homochirality
Desymmetrization of meso-Dibromocycloalkenes through Copper(I)-Catalyzed Asymmetric Allylic Substitution with Organolithium Reagents
The highly regio- and enantioselective (up to >99:1 dr, up to 99:1 er) desymmetrization of meso-1,4-dibromocycloalk-2-enes using asymmetric allylic substitution with organolithium reagents to afford enantioenriched bromocycloalkenes (ring size of 5 to 7) has been achieved. The cycloheptene products undergo an unusual ring contraction. The synthetic versatility of this Cu(I)-catalyzed reaction is demonstrated by the concise stereocontrolled preparation of cyclic amino alcohols, which are privileged chiral structures in natural products and pharmaceuticals and widely used in synthesis and catalysis
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