2,783 research outputs found
Instant Two-Body Equation in Breit Frame
A quasipotential formalism for elastic scattering from relativistic bound
states is based on applying an instant constraint to both initial and final
states in the Breit frame. This formalism is advantageous for the analysis of
electromagnetic interactions because current conservation and four momentum
conservation are realized within a three-dimensional formalism. Wave functions
are required in a frame where the total momentum is nonzero, which means that
the usual partial wave analysis is inapplicable. In this work, the
three-dimensional equation is solved numerically, taking into account the
relevant symmetries. A dynamical boost of the interaction also is needed for
the instant formalism, which in general requires that the boosted interaction
be defined as the solution of a four-dimensional equation. For the case of a
scalar separable interaction, this equation is solved and the Lorentz
invariance of the three-dimensional formulation using the boosted interaction
is verified. For more realistic interactions, a simple approximation is used to
characterize the boost of the interaction.Comment: 20 pages in revtex 3, 3 figures. Fixed reform/tex errors
Does tiny-scale atomic structure exist in the interstellar medium ?
We report on preliminary results from the recent multi-epoch neutral hydrogen
absorption measurements toward three pulsars, B0823+26, B1133+16 and B2016+28,
using the Arecibo telescope. We do not find significant variations in optical
depth profiles over periods of 0.3 and 9--10 yr, or on spatial scales of 10--20
and 70--85 AU. The large number of non detections of the tiny scale atomic
structure suggests that the AU-sized structure is not ubiquitous in the
interstellar medium and could be quite a rare phenomenon.Comment: Accepted by ApJ Letters, 5 pages, 2 figure
Electromagnetic Scattering from Relativistic Bound States
The quasipotential formalism for elastic scattering from relativistic bound
states is formulated based on the instant constraint in the Breit frame. The
quasipotential electromagnetic current is derived from Mandelstam's five-point
kernel and obeys a two-body Ward identity. Breit-frame wave functions are
obtained directly by solving integral equations with nonzero total
three-momentum, thus accomplishing a dynamical boost. Calculations of
electron-deuteron elastic form factors illustrate the importance of the
dynamical boost versus kinematic boosts of the rest frame wave functions.Comment: RevTeX 3.0 manuscript, 9 pages. UU-file is a single PostScript file
of the manuscript including figures. U. MD PP #93-17
Memetic Multilevel Hypergraph Partitioning
Hypergraph partitioning has a wide range of important applications such as
VLSI design or scientific computing. With focus on solution quality, we develop
the first multilevel memetic algorithm to tackle the problem. Key components of
our contribution are new effective multilevel recombination and mutation
operations that provide a large amount of diversity. We perform a wide range of
experiments on a benchmark set containing instances from application areas such
VLSI, SAT solving, social networks, and scientific computing. Compared to the
state-of-the-art hypergraph partitioning tools hMetis, PaToH, and KaHyPar, our
new algorithm computes the best result on almost all instances
Electron-deuteron scattering in the equal-time formalism: beyond the impulse approximation
Using a three-dimensional formalism that includes relativistic kinematics,
the effects of negative-energy states, approximate boosts of the two-body
system, and current conservation, we calculate the electromagnetic form factors
of the deuteron up to Q^2 of 4 GeV^2. This is done using a dynamical boost for
two-body systems with spin. We first compute form factors in impulse
approxmation, but then also add an isoscalar meson-exchange current of pion
range that involves the gamma-pi contact operator associated with pseudovector
pi-N coupling. We also consider effects of the rho-pi-gamma meson-exchange
current. The experimentally measured quantities A, B, and t20 are calculated
over the kinematic range probed in recent Jefferson Laboratory experiments. The
rho-pi-gamma meson-exchange current provides significant strength in A at large
Q^2 and the gamma-pi contact-term exchange current shifts t20, providing good
agreement with the JLab data. Relativistic effects and the gamma-pi
meson-exchange current do not provide an explanation of the B observable, but
the rho-pi-gamma current could help to provide agreement if a nonstandard value
is used for the tensor rho-N coupling that enters this contribution.Comment: 15 pages, 10 figures. (v2) Added references on rho-pi-gamma current
as well as comparison to recent Novosibirsk data on T20. Implemented
\includegraphics in place of \BoxedEPSF. (v3) Modified in order to clarify
the nature of the boost we implemented for particles with spin. Other minor
changes. Version to be published in Physical Review
Definitions, sources and self-reported consumption of regionally grown fruits and vegetables in two regions of Australia
Regional food systems are complex networks, with numerous retail sources that underpin a local economy. However, evidence is limited regarding how consumers define, identify, and source regionally grown fresh fruits and vegetables (RGFFV). A cross-sectional study was conducted in Tasmania (TAS) and South Western Australia (SWA) to compare how RGFFV are defined, identified and sourced by consumers, including self-reported consumption of selected RGFFV. Survey data were analyzed using the Chi-square test and t-tests. Results (TAS n = 120, SWA n= 123) identified that consumers had mixed perceptions of how RGFFV are defined, including produce sold at farmers markets, or grown within their region (TAS/SWA). RGFFV were commonly identified using product labelling (55% TAS, 69% SWA; p > 0.05). Respondents reported frequently shopping for RGFFV at major supermarkets, with more TAS respondents shopping weekly in comparison to SWA respondents (67% vs. 38%; p p = 0.012). The major RGFFV consumed were root vegetables and apples/pears, but consumers were frequently unsure about the produce's provenance. Our findings indicate multiple opportunities to improve consumption of fresh, regional produce in TAS and SWA, which may positively impact regional economic growth and community health
Confidential Boosting with Random Linear Classifiers for Outsourced User-generated Data
User-generated data is crucial to predictive modeling in many applications.
With a web/mobile/wearable interface, a data owner can continuously record data
generated by distributed users and build various predictive models from the
data to improve their operations, services, and revenue. Due to the large size
and evolving nature of users data, data owners may rely on public cloud service
providers (Cloud) for storage and computation scalability. Exposing sensitive
user-generated data and advanced analytic models to Cloud raises privacy
concerns. We present a confidential learning framework, SecureBoost, for data
owners that want to learn predictive models from aggregated user-generated data
but offload the storage and computational burden to Cloud without having to
worry about protecting the sensitive data. SecureBoost allows users to submit
encrypted or randomly masked data to designated Cloud directly. Our framework
utilizes random linear classifiers (RLCs) as the base classifiers in the
boosting framework to dramatically simplify the design of the proposed
confidential boosting protocols, yet still preserve the model quality. A
Cryptographic Service Provider (CSP) is used to assist the Cloud's processing,
reducing the complexity of the protocol constructions. We present two
constructions of SecureBoost: HE+GC and SecSh+GC, using combinations of
homomorphic encryption, garbled circuits, and random masking to achieve both
security and efficiency. For a boosted model, Cloud learns only the RLCs and
the CSP learns only the weights of the RLCs. Finally, the data owner collects
the two parts to get the complete model. We conduct extensive experiments to
understand the quality of the RLC-based boosting and the cost distribution of
the constructions. Our results show that SecureBoost can efficiently learn
high-quality boosting models from protected user-generated data
Australian consumer perceptions of regionally grown fruits and vegetables: importance, enablers, and barriers
Fresh fruits and vegetables are a cornerstone of a balanced diet; their consumption has health, environmental, ethical, and economic implications. This pilot study aimed to: (i) measure fruit and vegetable consumption; (ii) understand consumer perceptions of the perceived importance of regionally grown fresh fruit and vegetables (RGFFV); and (iii) identify the barriers and enablers of access and consumption of RGFFV. The study took place in Tasmania (TAS) and South Western Australia (SWA). A 54-item survey included questions relating to purchasing and consumption patterns; barriers and enablers related to access and consumption of RGFFV; and sociodemographic information. Survey data were analyzed using Chi-square test and binary logistic regression. A total of n = 120 TAS and n = 123 SWA adult respondents participated. SWA respondents had higher intakes of fruit (p p < 0.001). Almost all respondents (97%) rated purchasing of RGFFV as important. Top enablers included produce freshness (97%), and to financially support local farmers (94%) and the local community (91%). Barriers included limited seasonal availability of the produce (26%), the belief that RGFFV were expensive (12%) and food budgetary constraints (10%). Recommendations include broader marketing and labelling of seasonal RGFFV; increasing 'buy local' campaigns; consumer information about how RGFFV benefits producers and communities; and pricing produce according to quality
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