185 research outputs found
Internet communication among college students: its role and perceived effects on interaction and the self
This study is a qualitative investigation into the effect of internet technologies on the social lives of college students who frequently employ them. Three research questions are addressed. First, how do college students understand the various roles or functions of the Internet in terms of their social ties with others? Second, what problems related to interaction occur through the use of these communication technologies? Finally, what problems or effects related to the notion of "the self" occur when maintaining social ties via Internet communication technologies? Focus groups with college students indicated that they could not possibly imagine maintaining their social lives without them. Among the limitations and problems frequently indicated were a difficulty in using these communication options to discuss important, sensitive, or emotional issues with significant others. Finally, these college students appear to be more authentic online and less-fragmented by this form of communication than previous literature would suggest
A Theory of Spinning Particles for Large N_extended Supersymmetry (II)
Extending our prior investigation, we give a new off-shell construction of
theories of spinning particles propagating in Minkowski spaces with arbitrary
-extended supersymmetry on the world-line. The basis of the new off-shell
formulation is provided by realizations of new algebraic structures () that are certain generalizations of Pauli algebras.Comment: Latex file, 13 page
Non-Supersymmetric Loop Amplitudes and MHV Vertices
We show how the MHV diagram description of Yang-Mills theories can be used to
study non-supersymmetric loop amplitudes. In particular, we derive a compact
expression for the cut-constructible part of the general one-loop MHV
multi-gluon scattering amplitude in pure Yang-Mills theory. We show that in
special cases this expression reduces to known amplitudes - the amplitude with
adjacent negative-helicity gluons, and the five gluon non-adjacent amplitude.
Finally, we briefly discuss the twistor space interpretation of our result.Comment: 31 pages, 5 figures, Typos Correcte
The one-loop six-dimensional hexagon integral and its relation to MHV amplitudes in N=4 SYM
We provide an analytic formula for the (rescaled) one-loop scalar hexagon
integral with all external legs massless, in terms of classical
polylogarithms. We show that this integral is closely connected to two
integrals appearing in one- and two-loop amplitudes in planar
super-Yang-Mills theory, and . The derivative of
with respect to one of the conformal invariants yields
, while another first-order differential operator applied to
yields . We also introduce some kinematic
variables that rationalize the arguments of the polylogarithms, making it easy
to verify the latter differential equation. We also give a further example of a
six-dimensional integral relevant for amplitudes in
super-Yang-Mills.Comment: 18 pages, 2 figure
MHV Techniques for QED Processes
Significant progress has been made in the past year in developing new `MHV'
techniques for calculating multiparticle scattering amplitudes in Yang-Mills
gauge theories. Most of the work so far has focussed on applications to Quantum
Chromodynamics, both at tree and one-loop level. We show how such techniques
can also be applied to abelian theories such as QED, by studying the simplest
tree-level multiparticle process, e^+e^- to n \gamma. We compare explicit
results for up to n=5 photons using both the Cachazo, Svrcek and Witten `MHV
rules' and the related Britto-Cachazo-Feng `recursion relation' approaches with
those using traditional spinor techniques.Comment: 19 pages, 10 figures. References adde
Evidence for a Nonplanar Amplituhedron
The scattering amplitudes of planar N = 4 super-Yang-Mills exhibit a number of remarkable analytic structures, including dual conformal symmetry and logarithmic singularities of integrands. The amplituhedron is a geometric construction of the integrand that incorporates these structures. This geometric construction further implies the amplitude is fully specified by constraining it to vanish on spurious residues. By writing the amplitude in a dlog basis, we provide nontrivial evidence that these analytic properties and âzero conditionsâ carry over into the nonplanar sector. This suggests that the concept of the amplituhedron can be extended to the nonplanar sector of N = 4 super-Yang-Mills theory
Aggressive Aerial Grasping using a Soft Drone with Onboard Perception
Contrary to the stunning feats observed in birds of prey, aerial manipulation
and grasping with flying robots still lack versatility and agility.
Conventional approaches using rigid manipulators require precise positioning
and are subject to large reaction forces at grasp, which limit performance at
high speeds. The few reported examples of aggressive aerial grasping rely on
motion capture systems, or fail to generalize across environments and grasp
targets. We describe the first example of a soft aerial manipulator equipped
with a fully onboard perception pipeline, capable of robustly localizing and
grasping visually and morphologically varied objects. The proposed system
features a novel passively closing tendon-actuated soft gripper that enables
fast closure at grasp, while compensating for position errors, complying to the
target-object morphology, and dampening reaction forces. The system includes an
onboard perception pipeline that combines a neural-network-based semantic
keypoint detector with a state-of-the-art robust 3D object pose estimator,
whose estimate is further refined using a fixed-lag smoother. The resulting
pose estimate is passed to a minimum-snap trajectory planner, tracked by an
adaptive controller that fully compensates for the added mass of the grasped
object. Finally, a finite-element-based controller determines optimal gripper
configurations for grasping. Rigorous experiments confirm that our approach
enables dynamic, aggressive, and versatile grasping. We demonstrate fully
onboard vision-based grasps of a variety of objects, in both indoor and outdoor
environments, and up to speeds of 2.0 m/s -- the fastest vision-based grasp
reported in the literature. Finally, we take a major step in expanding the
utility of our platform beyond stationary targets, by demonstrating
motion-capture-based grasps of targets moving up to 0.3 m/s, with relative
speeds up to 1.5 m/s
Chagas Disease in the United States: a Public Health Approach.
Trypanosoma cruzi is the etiological agent of Chagas disease, usually transmitted by triatomine vectors. An estimated 20 to 30% of infected individuals develop potentially lethal cardiac or gastrointestinal disease. Sylvatic transmission cycles exist in the southern United States, involving 11 triatomine vector species and infected mammals such as rodents, opossums, and dogs. Nevertheless, imported chronic T. cruzi infections in migrants from Latin America vastly outnumber locally acquired human cases. Benznidazole is now FDA approved, and clinical and public health efforts are under way by researchers and health departments in a number of states. Making progress will require efforts to improve awareness among providers and patients, data on diagnostic test performance and expanded availability of confirmatory testing, and evidence-based strategies to improve access to appropriate management of Chagas disease in the United States
QCD Pressure at Two Loops in the Temporal Gauge
We apply the method of \underline{zeta} functions, together with the
-prescription for the temporal gauge, to evaluate the thermodynamic
pressure in QCD at finite temperature . Working in the imaginary-time
formalism and employing a special version of the unified-gauge prescription, we
show that the pure-gauge contribution to the pressure at two loops is given by
P_2^{\mbox{{\scriptsize gauge}}} = -(g^2/144)N_cN_gT^4, where and
denote the number of colours and gluons, respectively. This result agrees with
the value in the Feynman gauge.Comment: 19 pages, 2 figures, list of 63 integral
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