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Focus on nonlinear terahertz studies
Resulting from the availability of improved sources, research in the terahertz (THz) spectral range has increased dramatically over the last decade, leading essentially to the disappearance of the so-called 'THz gap'. While most work to date has been carried out with THz radiation of low field amplitude, a growing number of experiments are using THz radiation with large electric and magnetic fields that induce nonlinearities in the system under study. This 'focus on' collection contains a number of articles, both experimental and theoretical, in the new subfield of THz nonlinear optics and spectroscopy on various systems, among them molecular gases, superconductors, semiconductors, antiferromagnets and graphene
Preadolescent children's perception of power imbalance in bullying: A thematic analysis
Bullying in schools is associated with an extensive public health burden. Bullying is intentional and goal oriented aggressive behavior in which the perpetrator exploits an imbalance of power to repeatedly dominate the victim. To differentiate bullying from aggressive behavior, assessment must include a valid measure of power imbalance as perceived by the victim. And yet, to date, there remains no agreement as to how to most accurately measure power imbalance among preadolescent children. This qualitative study explored children's (age 9 to 11) understanding of power imbalance through thematic analysis of focus group discussions. Subthemes that emerged as influencing power imbalance include: Age of victim, peer valued characteristics, and group membership and position. Subthemes of empathy and peer valued characteristics emerged as protecting against the negative impact of power imbalance
The Phase Structure of Supersymmetric Sp(2N_c) Gauge Theories with an Adjoint
We study the phase structure of N = 1 supersymmetric Sp(2N_c) gauge theories
with 2N_f fundamentals, an adjoint, and vanishing superpotential. Using
a-maximization, we derive analytic expressions for the values of N_f below
which the first several gauge-invariant operators in the chiral ring violate
the unitarity bound and become free fields. In doing so we are able to
explicitly check previous conjectures about the behavior of this theory made by
Luty, Schmaltz, and Terning. We then compare this to an analysis of the first
two 'deconfined' dual descriptions based on the gauge groups Sp(2N_f+2) x
SO(2N_c+5) and Sp(2N_f+2) x SO(4N_f+4) x Sp(2N_c+2), finding precise agreement.
In particular, we find no evidence for non-obvious accidental symmetries or the
appearance of a mixed phase in which one of the dual gauge groups becomes free.Comment: 18 pages, 2 figures; v2: added references to match JHEP versio
Applicability of the Fisher Equation to Bacterial Population Dynamics
The applicability of the Fisher equation, which combines diffusion with
logistic nonlinearity, to population dynamics of bacterial colonies is studied
with the help of explicit analytic solutions for the spatial distribution of a
stationary bacterial population under a static mask. The mask protects the
bacteria from ultraviolet light. The solution, which is in terms of Jacobian
elliptic functions, is used to provide a practical prescription to extract
Fisher equation parameters from observations and to decide on the validity of
the Fisher equation.Comment: 5 pages, 3 figs. include
Experimental demonstration of a suspended diffractively coupled optical cavity
All-reflective optical systems are under consideration for future gravitational wave detector topologies. One approach in proposed designs is to use diffraction gratings as input couplers for Fabry–Perot cavities. We present an experimental demonstration of a fully suspended diffractively coupled cavity and investigate the use of conventional Pound–Drever–Hall length sensing and control techniques to maintain the required operating condition
Protecting the Baryon Asymmetry with Thermal Masses
We consider the evolution of baryon number in the early universe under
the influence of rapid sphaleron interactions and show that will remain
nonzero at all times even in the case of . This result arises due to
thermal Yukawa interactions that cause nonidentical dispersion relations
(thermal masses) for different lepton families. We point out the relevance of
our result to the Affleck-Dine type baryogenesis.Comment: 11pp., plain tex, UMN-TH-1248/94, CfPA-TH-94-1
Adaptation of Autocatalytic Fluctuations to Diffusive Noise
Evolution of a system of diffusing and proliferating mortal reactants is
analyzed in the presence of randomly moving catalysts. While the continuum
description of the problem predicts reactant extinction as the average growth
rate becomes negative, growth rate fluctuations induced by the discrete nature
of the agents are shown to allow for an active phase, where reactants
proliferate as their spatial configuration adapts to the fluctuations of the
catalysts density. The model is explored by employing field theoretical
techniques, numerical simulations and strong coupling analysis. For d<=2, the
system is shown to exhibits an active phase at any growth rate, while for d>2 a
kinetic phase transition is predicted. The applicability of this model as a
prototype for a host of phenomena which exhibit self organization is discussed.Comment: 6 pages 6 figur
Dark Matter with Dirac and Majorana Gaugino Masses
We consider the minimal supersymmetric extension of the Standard Model
allowing both Dirac and Majorana gauginos. The Dirac masses are obtained by
pairing up extra chiral multiplets: a singlet S for U(1)_Y, a triplet T for
SU(2) and an octet O for SU(3) with the respective gauginos. The electroweak
symmetry breaking sector is modified by the couplings of the new fields S and T
to the Higgs doublets. We discuss two limits: i) both the adjoint scalars are
decoupled with the main effect being the modification of the Higgs quartic
coupling; ii) the singlet remaining light, and due to its direct coupling to
sfermions, providing a new contribution to the soft masses and inducing new
decay/production channels. We discuss the LSP in this scenario; after
mentioning the possibility that it may be a Dirac gravitino, we focus on the
case where it is identified with the lightest neutralino, and exhibit
particular values of the parameter space where the relic density is in
agreement with WMAP data. This is illustrated for different scenarios where the
LSP is either a bino (in which case it can be a Dirac fermion) or
bino-higgsino/wino mixtures. We also point out in each case the peculiarity of
the model with respect to dark matter detection experiments.Comment: 43 pages, 5 figures; one reference added. Corresponds to published
version in JCA
Anion exchange membrane soil nitrate predicts turfgrass color and yield.
Desirable nitrogen (N) management practices for turfgrass supply sufficient N for high quality turf while limiting excess soil N. Previous studies suggested the potential of anion exchange membranes (AEMs) for predicting turfgrass color, quality, or yield. However, these studies suggested a wide range of critical soil nitrate-nitrogen (NO3-N) values across sample dates. A field experiment, in randomized complete block design with treatments consisting of nine N application rates, was conducted on a mixed species cool-season turfgrass lawn across two growing seasons. Every 2 wk from May to October, turfgrass color was assessed with three different reflectance meters, and soil NO3-N was measured with in situ AEMs. Cate-Nelson models were developed comparing relative reflectance value and yield to AEM desorbed soil NO3-N pooled across all sample dates. These models predicted critical AEM soil NO3-N values from 0. 45 to 1.4 micro g cm-2 d-1. Turf had a low probability of further positive response to AEM soil NO3-N greater than these critical values. These results suggest that soil NO3-N critical values from AEMs may be applicable across sample dates and years and may serve to guide N fertilization to limit excess soil NO3-N
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