58,485 research outputs found
Continuum theory of tilted chiral smectic phases
We demonstrate that the sequence of distorted commensurate phases observed in
tilted chiral smectics is explained by the gain in electrostatic energy due to
the lock-in of the unit cell to a number of layers which is the integer closest
to the ratio pitch over thickness of the subjacent Sm-C phase. We
also explain the sign change of the helicity in the middle of the sequence by a
balance between two twist sources one intrinsic and another due to the
distortion of the Sm-C
p-GaAs nanowire MESFETs with near-thermal limit gating
Difficulties in obtaining high-performance p-type transistors and gate
insulator charge-trapping effects present two major challenges for III-V
complementary metal-oxide semiconductor (CMOS) electronics. We report a p-GaAs
nanowire metal-semiconductor field-effect transistor (MESFET) that eliminates
the need for a gate insulator by exploiting the Schottky barrier at the
metal-GaAs interface. Our device beats the best-performing p-GaSb nanowire
metal-oxide-semiconductor field effect transistor (MOSFET), giving a typical
sub-threshold swing of 62 mV/dec, within 4% of the thermal limit, on-off ratio
, on-resistance ~700 k, contact resistance ~30 k,
peak transconductance 1.2 S/m and high-fidelity ac operation at
frequencies up to 10 kHz. The device consists of a GaAs nanowire with an
undoped core and heavily Be-doped shell. We carefully etch back the nanowire at
the gate locations to obtain Schottky-barrier insulated gates whilst leaving
the doped shell intact at the contacts to obtain low contact resistance. Our
device opens a path to all-GaAs nanowire MESFET complementary circuits with
simplified fabrication and improved performance
La théorie marxiste du salaire
This article develops and discusses the foundations of the marxist wage-theory. According to this theory, the labor force is a commodity, so it has a use value and an exchange value. Exchange value becomes a price and the wage, on a market, becomes the labor market. A detailed examination of these statements leads to several critical remarks. The main one is that the theory cannot describe and explain the contents of the value of the labor force and is unable to understand how the exchange value of labor force is changing in a price: the wage. That is a fundamental critique from the marxist epistemologic point of view, which needs a radical reconstruction of the theory
La théorie marxiste du salaire
This article develops and discusses the foundations of the marxist wage-theory. According to this theory, the labor force is a commodity, so it has a use value and an exchange value. Exchange value becomes a price and the wage, on a market, becomes the labor market.
Damping by slow relaxing rare earth impurities in Ni80Fe20
Doping NiFe by heavy rare earth atoms alters the magnetic relaxation
properties of this material drastically. We show that this effect can be well
explained by the slow relaxing impurity mechanism. This process is a
consequence of the anisotropy of the on site exchange interaction between the
4f magnetic moments and the conduction band. As expected from this model the
magnitude of the damping effect scales with the anisotropy of the exchange
interaction and increases by an order of magnitude at low temperatures. In
addition our measurements allow us to determine the relaxation time of the 4f
electrons as a function of temperature
Why polymer chains in a melt are not random walks
A cornerstone of modern polymer physics is the `Flory ideality hypothesis'
which states that a chain in a polymer melt adopts `ideal' random-walk-like
conformations. Here we revisit theoretically and numerically this pivotal
assumption and demonstrate that there are noticeable deviations from ideality.
The deviations come from the interplay of chain connectivity and the
incompressibility of the melt, leading to an effective repulsion between chain
segments of all sizes . The amplitude of this repulsion increases with
decreasing where chain segments become more and more swollen. We illustrate
this swelling by an analysis of the form factor , i.e. the scattered
intensity at wavevector resulting from intramolecular interferences of a
chain. A `Kratky plot' of {\em vs.} does not exhibit the plateau
for intermediate wavevectors characteristic of ideal chains. One rather finds a
conspicuous depression of the plateau, ,
which increases with and only depends on the monomer density .Comment: 4 pages, 4 figures, EPL, accepted January 200
Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
RSFQ devices with selective dissipation for quantum information processing
We study the possibility to use frequency dependent damping in RSFQ circuits
as means to reduce dissipation and consequent decoherence in RSFQ/qubit
circuits. We show that stable RSFQ operation can be achieved by shunting the
Josephson junctions with an circuit instead of a plain resistor. We derive
criteria for the stability of such an arrangement, and discuss the effect on
decoherence and the optimisation issues. We also design a simple flux generator
aimed at manipulating flux qubits
The Nature of the Giant Outbursts in the Bursting Pulsar GRO J 1744-28
We investigate the possible role of an accretion disk instability in
producing the giant outbursts seen in GRO J1744-28. Specifically, we study the
global, time dependent evolution of the Lightman-Eardley instability which can
develop near the inner edge of an accretion disk when the radiation pressure
becomes comparable to the gas pressure. Broadly speaking, our results are
compatible with earlier works by Taam \& Lin and by Lasota \& Pelat. The
uniqueness of GRO J1744-28 appears to be associated with the constraint that,
in order for outbursts to occur, the rate of accretion at the inner edge must
be within a narrow range just above the critical accretion rate at which
radiation pressure is beginning to become significant.Comment: 11 pages in .tex file, 4 Postscript figures, .tex file uses
aasms.sty; Ap. J. L. 1996, in pres
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