93,388 research outputs found
Strong Hall voltage modulation in hybrid ferromagnet/semiconductor microstructures
We present a new magnetoelectronic device consisting of a µm-scale semiconductor cross junction and a patterned, electrically isolated, ferromagnetic overlayer with in-plane magnetization. The large local magnetic field emanating from the edge of the thin ferromagnetic film has a strong perpendicular magnetic component, B[perpendicular](r), which induces a Hall resistance, RH, in the microjunction. External application of a weak in-plane magnetic field reverses the magnetization of the ferromagnet and with it B[perpendicular](r), thus modulating RH. Our data demonstrate that this strong "local" Hall effect is operative at both cryogenic and room temperatures, and is promising for device applications such as field sensors or integrated nonvolatile memory cells
From market games to real-world markets
This paper uses the development of multi-agent market models to present a
unified approach to the joint questions of how financial market movements may
be simulated, predicted, and hedged against. We examine the effect of different
market clearing mechanisms and show that an out-of-equilibrium clearing process
leads to dynamics that closely resemble real financial movements. We then show
that replacing the `synthetic' price history used by these simulations with
data taken from real financial time-series leads to the remarkable result that
the agents can collectively learn to identify moments in the market where
profit is attainable. We then employ the formalism of Bouchaud and Sornette in
conjunction with agent based models to show that in general risk cannot be
eliminated from trading with these models. We also show that, in the presence
of transaction costs, the risk of option writing is greatly increased. This
risk, and the costs, can however be reduced through the use of a delta-hedging
strategy with modified, time-dependent volatility structure.Comment: Presented at APFA2 (Liege) July 2000. Proceedings: Eur. Phys. J. B
Latex file + 10 .ps figs. [email protected]
Behavioural interventions for weight management in pregnancy: A systematic review of quantitative and qualitative data
Objective: To assess the effectiveness of dietary with or without physical activity interventions to prevent excessive weight gain in pregnancy and explore the factors that influence intervention effectiveness.
Design: Systematic review, including a meta-analysis of controlled trials of interventions to prevent excessive weight gain during pregnancy and a thematic synthesis of qualitative studies that investigated the views of women on weight management during pregnancy.
Data sources: Eleven electronic bibliographic databases, reference list of included studies, relevant review articles and experts in the field.
Review methods: Two independent reviewers extracted data. RevMan software was used to perform the meta-analyses. Qualitative data was subject to thematic analysis. Both quantitative and qualitative data were aligned using a matrix framework.
Results: Five controlled trials and nine qualitative studies were included. The overall pooled effect size found no significant difference in gestational weight gain amongst participants in the interventions group compared with the control group (mean difference -1.88kg CI -4.34 to 0.59). The study designs, participants and interventions all varied markedly and there was significant heterogeneity within this comparison in the meta-analysis (I2 76%). Subgroup and sensitivity analysis did not identify contextual elements that influenced the effectiveness of the intervention.
In a thematic analysis of the qualitative studies, three major themes emerged relating to women’s views of weight management in pregnancy; pregnancy as a time of transition and change, conflicting and contradictory messages, a perceived lack of control. When the results of both quantitative and qualitative data were aligned it was clear that some of the barriers that women described in achieving healthy weight gain in pregnancy were not addressed by the interventions evaluated. This may have contributed to the limited effectiveness of the interventions.
Conclusions: Despite intense and often tailored interventions there was no statistically significant effect on weight gain during pregnancy. Inadequate and often contradictory information regarding healthy weight management was reported by women in qualitative studies and this was addressed in the interventions but in itself was insufficient to lead to reduced weight gain. Multiple types of interventions, including community based strategies, are needed to address this complex health problem
Design, development and fabrication of a Precision Autocollimating Solar Sensor /PASS/
Precision Autocollimating Solar Sensor /PASS/ for Solar Pointing Aerobee Rocket Control System /SPARCS/ progra
Multi-Agent Complex Systems and Many-Body Physics
Multi-agent complex systems comprising populations of decision-making
particles, have many potential applications across the biological,
informational and social sciences. We show that the time-averaged dynamics in
such systems bear a striking resemblance to conventional many-body physics. For
the specific example of the Minority Game, this analogy enables us to obtain
analytic expressions which are in excellent agreement with numerical
simulations.Comment: Accepted for publication in Europhysics Letter
The effect of clouds on the earth's radiation balance
The effect of global cloudiness on the radiation balance at the top of the atmosphere is studied in general circulation model experiments. Wintertime simulations were conducted with clouds that had realistic optical properties, and were compared with simulations in which the clouds were transparent to either solar or thermal radiation. Clouds increase the net balance by limiting longwave loss to space, but decrease it by reflecting solar radiation. It is found that the net result of cloudiness is to maintain net radiation which is less than would be realized under clear conditions: Clouds cause the net radiation at the top of the atmosphere to increase due to longwave absorption, but to decrease even more due to cloud reflectance of solar radiation
Potential formulation of the dispersion relation for a uniform, magnetized plasma with stationary ions in terms of a vector phasor
The derivation of the helicon dispersion relation for a uniform plasma with
stationary ions subject to a constant background magnetic field is reexamined
in terms of the potential formulation of electrodynamics. Under the same
conditions considered by the standard derivation, the nonlinear self-coupling
between the perturbed electron flow and the potential it generates is
addressed. The plane wave solution for general propagation vector is determined
for all frequencies and expressed in terms of a vector phasor. The behavior of
the solution as described in vacuum units depends upon the ratio of
conductivity to the magnitude of the background field. Only at low conductivity
and below the cyclotron frequency can significant propagation occur as
determined by the ratio of skin depth to wavelength.Comment: 10 pages, 6 figures, major revision, final version, to appear in Po
Helicity supersymmetry of dyons
The 'dyon' system of D'Hoker and Vinet consisting of a spin 1/2 particle with
anomalous gyromagnetic ratio 4 in the combined field of a Dirac monopole plus a
Coulomb plus a suitable potential (which arises in the long-range limit
of a self-dual monopole) is studied following Biedenharn's approach to the
Dirac-Coulomb problem: the explicit solution is obtained using the
`Biedenharn-Temple operator', , and the extra two-fold degeneracy is
explained by the subtle supersymmetry generated by the 'Dyon Helicity' or
generalized `Biedenharn-Johnson-Lippmann' operator . The new SUSY
anticommutes with the chiral SUSY discussed previously.Comment: 14 pages, 2 figure
Theory of adhesion: role of surface roughness
We discuss how surface roughness influence the adhesion between elastic
solids. We introduce a Tabor number which depends on the length scale or
magnification, and which gives information about the nature of the adhesion at
different length scales. We consider two limiting cases relevant for (a)
elastically hard solids with weak adhesive interaction (DMT-limit) and (b)
elastically soft solids or strong adhesive interaction (JKR-limit). For the
former cases we study the nature of the adhesion using different adhesive force
laws (, , where is the wall-wall separation). In
general, adhesion may switch from DMT-like at short length scales to JKR-like
at large (macroscopic) length scale. We compare the theory predictions to the
results of exact numerical simulations and find good agreement between theory
and the simulation results
- …