3,504 research outputs found
Temperature-stable Gunn-diode oscillator
Oscillator consisting of Gunn diode embedded in coaxial circuit has excellent temperature stability and low fabrication costs as compared with automatic-frequency-control crystal oscillators
Sound propagation in density wave conductors and the effect of long-range Coulomb interaction
We study theoretically the sound propagation in charge- and spin-density
waves in the hydrodynamic regime. First, making use of the method of comoving
frame, we construct the stress tensor appropriate for quasi-one dimensional
systems within tight-binding approximation. Taking into account the screening
effect of the long-range Coulomb interaction, we find that the increase of the
sound velocity below the critical temperature is about two orders of magnitude
less for longitudinal sound than for transverse one. It is shown that only the
transverse sound wave with displacement vector parallel to the chain direction
couples to the phason of the density wave, therefore we expect significant
electromechanical effect only in this case.Comment: revtex, 14 pages (in preprint form), submitted to PR
Recent Advances in Unconventional Density Waves
Unconventional density wave (UDW) has been speculated as a possible
electronic ground state in excitonic insulator in 1968. Recent surge of
interest in UDW is partly due to the proposal that the pseudogap phase in high
T_c cuprate superconductors is d-wave density wave (d-DW).
Here we review our recent works on UDW within the framework of mean field
theory. In particular we have shown that many properties of the low temperature
phase (LTP) in alpha-(BEDT-TTF)_2MHg(SCN)_4 with M=K, Rb and Tl are well
characterized in terms of unconventional charge density wave (UCDW). In this
identification the Landau quantization of the quasiparticle motion in a
magnetic field (the Nersesyan effect) plays the crucial role. Indeed the
angular dependent magnetoresistance and the negative giant Nernst effect are
two hallmarks of UDW.Comment: 18 pages, 12 figure
Combined Electroweak Analysis
Recent developments in the measurement of precision electroweak measurements
are summarised, notably new results on the mass of the top quark and mass and
width of the W boson. Predictions of the Standard Model are compared to the
experimental results which are used to constrain the input parameters of the
Standard Model, in particular the mass of the Higgs boson. The agreement
between measurements and expectations from theory is discussed.
Invited talk presented at the EPS HEP 2007 conference
Manchester, England, July 19th to 25th, 2007Comment: 7 pages and 6 figure
Magneto-Hydrodynamics of Population III Star Formation
Jet driving and fragmentation process in collapsing primordial cloud are
studied using three-dimensional MHD nested grid simulations. Starting from a
rotating magnetized spherical cloud with the number density of n=10^3 cm^-3, we
follow the evolution of the cloud up to the stellar density n=10^22 cm^-3. We
calculate 36 models parameterizing the initial magnetic and rotational energies
(\gamma_0, \beta_0). In the collapsing primordial clouds, the cloud evolutions
are characterized by the ratio of the initial rotational to magnetic energy,
\gamma_0/\beta_0. The Lorentz force significantly affects the cloud evolution
when \gamma_0 > \beta_0, while the centrifugal force is more dominant than the
Lorentz force when \beta_0 > \gamma_0. When the cloud rotates rapidly with
angular velocity of \Omega_0 > 10^-17 (n/10^3 cm^-3)^2/3 s^-1 and \beta_0 >
\gamma_0, fragmentation occurs before the protostar is formed, but no jet
appears after the protostar formation. On the other hand, a strong jet appears
after the protostar formation without fragmentation when the initial cloud has
the magnetic field of B_0 > 10^-9 (n/10^3 cm^-3)^2/3 G and \gamma_0 > \beta_0.
Our results indicate that proto-Population III stars frequently show
fragmentation and protostellar jet. Population III stars are therefore born as
binary or multiple stellar systems, and they can drive strong jets, which
disturb the interstellar medium significantly, as well as in the present-day
star formation, and thus they may induce the formation of next generation
stars.Comment: 37 pages, 10 figures, Submitted to ApJ, For high resolution figures,
see http://astro3.sci.hokudai.ac.jp/~machida/astro-ph.pd
Neutrino Mixing and Leptonic CP Phase in Neutrino Oscillations
Oscillations of the Dirac neutrinos of three generations in vacuum are
considered with allowance made for the effect of the CP-violating leptonic
phase (analogue of the quark CP phase) in the lepton mixing matrix. The general
formulas for the probabilities of neutrino transition from one sort to another
in oscillations are obtained as functions of three mixing angles and the CP
phase. It is found that the leptonic CP phase can, in principle, be
reconstructed by measuring the oscillation-averaged probabilities of neutrino
transition from one sort to another. The manifestation of the CP phase as a
deviation of the probabilities of direct processes from those of inverse
processes is an effect that is practically unobservable as yet
Glucose metabolism and oscillatory behavior of pancreatic islets
A variety of oscillations are observed in pancreatic islets.We establish a
model, incorporating two oscillatory systems of different time scales: One is
the well-known bursting model in pancreatic beta-cells and the other is the
glucose-insulin feedback model which considers direct and indirect feedback of
secreted insulin. These two are coupled to interact with each other in the
combined model, and two basic assumptions are made on the basis of biological
observations: The conductance g_{K(ATP)} for the ATP-dependent potassium
current is a decreasing function of the glucose concentration whereas the
insulin secretion rate is given by a function of the intracellular calcium
concentration. Obtained via extensive numerical simulations are complex
oscillations including clusters of bursts, slow and fast calcium oscillations,
and so on. We also consider how the intracellular glucose concentration depends
upon the extracellular glucose concentration, and examine the inhibitory
effects of insulin.Comment: 11 pages, 16 figure
Time-Dependent Multi-Centre Solutions from New Metrics with Holonomy Sim(n-2)
The classifications of holonomy groups in Lorentzian and in Euclidean
signature are quite different. A group of interest in Lorentzian signature in n
dimensions is the maximal proper subgroup of the Lorentz group, SIM(n-2).
Ricci-flat metrics with SIM(2) holonomy were constructed by Kerr and Goldberg,
and a single four-dimensional example with a non-zero cosmological constant was
exhibited by Ghanam and Thompson. Here we reduce the problem of finding the
general -dimensional Einstein metric of SIM(n-2) holonomy, with and without
a cosmological constant, to solving a set linear generalised Laplace and
Poisson equations on an (n-2)-dimensional Einstein base manifold. Explicit
examples may be constructed in terms of generalised harmonic functions. A
dimensional reduction of these multi-centre solutions gives new time-dependent
Kaluza-Klein black holes and monopoles, including time-dependent black holes in
a cosmological background whose spatial sections have non-vanishing curvature.Comment: Typos corrected; 29 page
Charge-density Waves Survive the Pauli Paramagnetic Limit
Measurements of the resistance of single crystals of (Per)Au(mnt)
have been made at magnetic fields of up to 45 T, exceeding the Pauli
paramagnetic limit of T. The continued presence of
non-linear charge-density wave electrodynamics at T unambiguously
establishes the survival of the charge-density wave state above the Pauli
paramagnetic limit, and the likely emergence of an inhomogeneous phase
analogous to that anticipated to occur in superconductors.Comment: 4 pages, three figure
- …