4,790 research outputs found
Channel-wall limitations in the magnetohydrodynamic induction generator
Discussion of magnetohydrodynamic induction generator examines the machine in detail and materials problems influencing its design. The higher upper-temperature limit of the MHD system promises to be more efficient than present turbine systems for generating electricity
Renormalization Group Study of the Intrinsic Finite Size Effect in 2D Superconductors
Vortices in a thin-film superconductor interact logarithmically out to a
distance on the order of the two-dimensional (2D) magnetic penetration depth
, at which point the interaction approaches a constant. Thus,
because of the finite , the system exhibits what amounts to an
{\it intrinsic} finite size effect. It is not described by the 2D Coulomb gas
but rather by the 2D Yukawa gas (2DYG). To study the critical behavior of the
2DYG, we map the 2DYG to the massive sine-Gordon model and then perform a
renormalization group study to derive the recursion relations and to verify
that is a relevant parameter. We solve the recursion relations
to study important physical quantities for this system including the
renormalized stiffness constant and the correlation length. We also address the
effect of current on this system to explain why finite size effects are not
more prevalent in experiments given that the 2D magnetic penetration depth is a
relevant parameter.Comment: 8 pages inRevTex, 5 embedded EPS figure
Sixty-GHz integrated RF head Final report
Integrated 60.8 GHz RF receiver and low noise IF preamplifier developmen
Transverse and secondary voltages in BSCCO single crystals
Multicontact configuration is one of the most powerful arrangements for
electrical transport measurements applied to study vortex phase transition and
vortex phase dimensionality in strongly anisotropic high-Tc superconducting
materials. In this paper we present electrical transport measurements using a
multiterminal configuration, which prove both the existence of guided vortex
motion in BSCCO single crystals near the transition temperature and that
secondary voltage in zero external magnetic field is induced by thermally
activated vortex loop unbinding. The phase transition between the bound and
unbound states of the vortex loops was found to be below the temperature where
the phase coherence of the superconducting order parameter extends over the
whole volume of the sample. We show experimentally that 3D/2D phase transition
in vortex dimensionality is a length-scale-dependent layer decoupling process
and takes place simultaneously with the 3D/2D phase transition in
superconductivity at the same temperature.Comment: 8 pages, 5 figures, to be published in Physica
Renormalization-Group Analysis of Layered Sine-Gordon Type Models
We analyze the phase structure and the renormalization group (RG) flow of the
generalized sine-Gordon models with nonvanishing mass terms, using the
Wegner-Houghton RG method in the local potential approximation. Particular
emphasis is laid upon the layered sine-Gordon (LSG) model, which is the
bosonized version of the multi-flavour Schwinger model and approaches the sum
of two ``normal'', massless sine-Gordon (SG) models in the limit of a vanishing
interlayer coupling J. Another model of interest is the massive sine-Gordon
(MSG) model. The leading-order approximation to the UV (ultra-violet) RG flow
predicts two phases for the LSG as well as for the MSG, just as it would be
expected for the SG model, where the two phases are known to be separated by
the Coleman fixed point. The presence of finite mass terms (for the LSG and the
MSG) leads to corrections to the UV RG flow, which are naturally identified as
the ``mass corrections''. The leading-order mass corrections are shown to have
the following consequences: (i) for the MSG model, only one phase persists, and
(ii) for the LSG model, the transition temperature is modified. Within the
mass-corrected UV scaling laws, the limit of J -> 0 is thus nonuniform with
respect to the phase structure of the model. The modified phase structure of
general massive sine-Gordon models is connected with the breaking of symmetries
in the internal space spanned by the field variables. For the LSG, the
second-order subleading mass corrections suggest that there exists a cross-over
regime before the IR scaling sets in, and the nonlinear terms show explicitly
that higher-order Fourier modes appear in the periodic blocked potential.Comment: 27 pages, 7 figure
Raspberry Pi VPN Travel Router
Consumers are increasingly relying on public wireless hotspots to access the internet from a growing number of devices. Usage of these hotspots has expanded from just laptops to everything from iPhones to tablets, which are expected to be internet-connected for full functionality. It has become common for one to check if there’s an open wireless hotspot connection available at places like coffee shops, hotels, restaurants, or even a doctor’s waiting room. The issue that arises is that these public connections present an inherent security risk, as anyone can connect and gain access to the network. For increased security, the use of a Virtual Private Network (VPN) is often recommended while connected to a public network, especially for sensitive data. Individuals can choose from a variety of VPN providers today, but are usually required to download a software client for each of their devices they want to connect to the VPN.
My project involves the use of a Raspberry Pi serving as a VPN router to provide secure internet access for connected devices. The Pi is connected to the internet via either a wireless or wired ethernet interface, and in turn provides a VPN connection through a wireless access point. When a computer or mobile device connects to the Pi, all traffic is routed through the VPN tunnel before reaching the internet. No software client is required for devices to connect as the Pi handles connecting to the VPN service and all required routing. Any number of devices with different operating systems can utilize the Pi’s secure network, as the process is no different than accessing a standard wireless access point
Some examples of deep structure of the Archean from geophysics
The development of Archean crust remains as one of the significant problems in earth science, and a major unknown concerning Archean terrains is the nature of the deep crust. The character of crust beneath granulite terrains is especially fascinating because granulites are generally interpreted to represent a deep crustal section. Magnetic data from this area can be best modeled with a magnetized wedge of older Archean rocks (granulitic gneisses) underlying the younger Archean greenstone terrain. The dip of the boundary based on magnetic modeling is the same as the dip of the postulated thrust-fault reflection. Thus several lines of evidence indicate that the younger Archean greenstone belt terrain is thrust above the ancient Minnesota Valley gneiss terrain, presumably as the greenstone belt was accreted to the gneiss terrain, so that the dipping reflection represents a suture zone. Seismic data from underneath the granulite-facies Minnesota gneiss terrain shows abundant reflections between 3 and 6 s, or about 9 to 20 km. These are arcuate or dipping multicyclic events indicative of layering
The Current-Temperature Phase Diagram of Layered Superconductors
The behavior of clean layered superconductors in the presence of a finite
electric current and in zero-magnetic field behavior is addressed. The
structure of the current temperature phase diagram and the properties of each
of the four regions will be explained. We will discuss the expected current
voltage and resistance characteristics of each region as well as the effects of
finite size and weak disorder on the phase diagram. In addition, the reason for
which a weakly non-ohmic region exists above the transition temperature will be
explained.Comment: 8 pages (RevTeX), 4 encapsulated postscript figure
Some applications of radar return data to the study of terrestrial and oceanic phenomena
Side-looking radar spacecraft application to mapping, imagery, altimetry, geology, pedology, glaciology, agriculture, and oceanograph
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