95,603 research outputs found
The impact of college student immersion service learning trips on coping with stress and vocational identity
This study examined the impact of service learning immersion trips on vocational identity and coping with stress among college students. Fifty-one students (15 males, 36 females) who participated in immersion trips and 76 students (25 males, 51 females) in a non-immersion control group completed a series of questionnaires directly before and immediately after both fall and spring break immersion trips, and during a four-month follow up. Results suggest that, after returning from an immersion trip, students report a greater ability to cope with stress and a somewhat stronger sense of vocational identity relative to students who do not participate in immersion trips
A model for the Delta(1600) resonance and gamma N -> Delta(1600) transition
A covariant spectator constituent quark model is applied to study the gamma N
-> Delta(1600) transition. Two processes are important in the transition: a
photon couples to the individual quarks of the Delta(1600) core (quark core),
and a photon couples to the intermediate pion-baryon states (pion cloud). While
the quark core contributions are estimated assuming Delta(1600) as the first
radial excitation of Delta(1232), the pion cloud contributions are estimated
based on an analogy with the gamma N -> Delta(1232) transition. To estimate the
pion cloud contributions in the gamma N -> Delta(1600) transition, we include
the relevant intermediate states, pi-N, pi-Delta, pi-N(1440) and
pi-Delta(1600). Dependence on the four-momentum transfer squared, Q2, is
predicted for the magnetic dipole transition form factor, GM*(Q2), as well as
the helicity amplitudes, A_1/2(Q2) and A_3/2(Q2). The results at Q2=0 are
compared with the existing data.Comment: To appear in Phys. Rev. D. Version with small modifications. 14
pages, 6 figures and 3 table
Scale-free networks in complex systems
In the past few years, several studies have explored the topology of
interactions in different complex systems. Areas of investigation span from
biology to engineering, physics and the social sciences. Although having
different microscopic dynamics, the results demonstrate that most systems under
consideration tend to self-organize into structures that share common features.
In particular, the networks of interaction are characterized by a power law
distribution, , in the number of connections per node,
, over several orders of magnitude. Networks that fulfill this propriety of
scale-invariance are referred to as ``scale-free''. In the present work we
explore the implication of scale-free topologies in the antiferromagnetic (AF)
Ising model and in a stochastic model of opinion formation. In the first case
we show that the implicit disorder and frustration lead to a spin-glass phase
transition not observed for the AF Ising model on standard lattices. We further
illustrate that the opinion formation model produces a coherent, turbulent-like
dynamics for a certain range of parameters. The influence, of random or
targeted exclusion of nodes is studied.Comment: 9 pages, 4 figures. Proceeding to "SPIE International Symposium
Microelectronics, MEMS, and Nanotechnology", 11-15 December 2005, Brisbane,
Australi
Quorum-quenching activity of the AHL-lactonase from <i>Bacillus licheniformis</i> DAHB1 inhibits vibrio biofilm formation in vitro and reduces shrimp intestinal colonisation and mortality
Vibrio parahaemolyticus is a significant cause of gastroenteritis resulting from the consumption of undercooked sea foods and often cause significant infections in shrimp aquaculture. Vibrio virulence is associated with biofilm formation and is regulated by N-acylated homoserine lactone (AHL)-mediated quorum sensing. In an attempt to reduce vibrio colonisation of shrimps and mortality, we screened native intestinal bacilli from Indian white shrimps (Fenneropenaeus indicus) for an isolate which showed biofilm-inhibitory activity (quorum quenching) against the pathogen V. parahaemolyticus DAHP1. The AHL-lactonase (AiiA) expressed by one of these, Bacillus licheniformis DAHB1, was characterised as having a broad-spectrum AHL substrate specificity and intrinsic resistance to the acid conditions of the shrimp intestine. Purified recombinant AiiA inhibited vibrio biofilm development in a cover slip assay and significantly attenuated infection and mortality in shrimps reared in a recirculation aquaculture system. Investigation of intestinal samples also showed that AiiA treatment also reduced vibrio viable counts and biofilm development as determined by confocal laser scanning microscopy (CLSM) imaging. These findings suggest that the B. licheniformis DAHB1 quorum-quenching AiiA might be developed for use as a prophylactic treatment to inhibit or reduce vibrio colonisation and mortality of shrimps in aquaculture
Modeling of primary dendrite arm spacing variations in thin-slab casting of low carbon and low alloy steels
Solidification structure of a High Strength Low Alloy (HSLA) steel, in terms of dendrite arm spacing distribution across the shell thickness, is studied in a breakout shell from a thin-slab caster at Tata Steel in IJmuiden. Columnar dendrites were found to be the predominant morphology throughout the shell with size variations across the shell thickness. Primary Dendrite Arm Spacing (PDAS) increases by increasing the distance from meniscus or slab surface. Subsequently, a model is proposed to describe the variation of the PDAS with the shell thickness (the distance from slab surface) under solidifiction conditions experienced in the primary cooling zone of thin-slab casting. The proposed relationship related the PDAS to the shell thickness and, hence, can be used as a tool for predicting solidifcation structure and optimizing the thin-slab casting of low alloy steels
Liquid-gas phase transition in nuclear matter including strangeness
We apply the chiral SU(3) quark mean field model to study the properties of
strange hadronic matter at finite temperature. The liquid-gas phase transition
is studied as a function of the strangeness fraction. The pressure of the
system cannot remain constant during the phase transition, since there are two
independent conserved charges (baryon and strangeness number). In a range of
temperatures around 15 MeV (precise values depending on the model used) the
equation of state exhibits multiple bifurcates. The difference in the
strangeness fraction between the liquid and gas phases is small when they
coexist. The critical temperature of strange matter turns out to be a
non-trivial function of the strangeness fraction.Comment: 15 pages, 7 figure
Phase transition from quark-meson coupling hyperonic matter to deconfined quark matter
We investigate the possibility and consequences of phase transitions from an
equation of state (EOS) describing nucleons and hyperons interacting via mean
fields of sigma, omega, and rho mesons in the recently improved quark-meson
coupling (QMC) model to an EOS describing a Fermi gas of quarks in an MIT bag.
The transition to a mixed phase of baryons and deconfined quarks, and
subsequently to a pure deconfined quark phase, is described using the method of
Glendenning. The overall EOS for the three phases is calculated for various
scenarios and used to calculate stellar solutions using the
Tolman-Oppenheimer-Volkoff equations. The results are compared with recent
experimental data, and the validity of each case is discussed with consequences
for determining the species content of the interior of neutron stars.Comment: 12 pages, 14 figures; minor typos correcte
Coherent control of plasma dynamics
Coherent control of a system involves steering an interaction to a final
coherent state by controlling the phase of an applied field. Plasmas support
coherent wave structures that can be generated by intense laser fields. Here,
we demonstrate the coherent control of plasma dynamics in a laser wakefield
electron acceleration experiment. A genetic algorithm is implemented using a
deformable mirror with the electron beam signal as feedback, which allows a
heuristic search for the optimal wavefront under laser-plasma conditions that
is not known a priori. We are able to improve both the electron beam charge and
angular distribution by an order of magnitude. These improvements do not simply
correlate with having the `best' focal spot, since the highest quality vacuum
focal spot produces a greatly inferior electron beam, but instead correspond to
the particular laser phase that steers the plasma wave to a final state with
optimal accelerating fields
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