68,074 research outputs found
Adsorption assisted translocation of a chain molecule through a pore in a spherical vesicle
We analyze the free energy for translocation of a polymer from the outside of
a spherical vesicle to the inside. The process is assumed to be driven by the
adsorption of the polymer on the inner surface of the vesicle. We argue that in
the case where the polymer is adsorbed on the outer surface too, the entropic
barrier for translocation is absent. We analyze the adsorption energy and find
the free energy profile for the process. We argue that the motion corresponds
to a polymer crossing a region with a change in free energy per segment. Based
upon our earlier analsis of the behaviour of kinks in such a problem, we
conclude that the translocation can occur with a crossing time
Unparticle Searches Through Low Energy Parity Violating Asymmetry
In this paper, we study the effects of the unparticles on the
parity-violating asymmetry for the low energy electron-electron scattering,
. Using the data from the E158 experiment at SLAC we
extract the limits on the unparticle coupling , and on the the
energy scale at 95% C.L. for various values of the scaling dimension
Asymptotic Performance of Linear Receivers in MIMO Fading Channels
Linear receivers are an attractive low-complexity alternative to optimal
processing for multi-antenna MIMO communications. In this paper we characterize
the information-theoretic performance of MIMO linear receivers in two different
asymptotic regimes. For fixed number of antennas, we investigate the limit of
error probability in the high-SNR regime in terms of the Diversity-Multiplexing
Tradeoff (DMT). Following this, we characterize the error probability for fixed
SNR in the regime of large (but finite) number of antennas.
As far as the DMT is concerned, we report a negative result: we show that
both linear Zero-Forcing (ZF) and linear Minimum Mean-Square Error (MMSE)
receivers achieve the same DMT, which is largely suboptimal even in the case
where outer coding and decoding is performed across the antennas. We also
provide an approximate quantitative analysis of the markedly different behavior
of the MMSE and ZF receivers at finite rate and non-asymptotic SNR, and show
that while the ZF receiver achieves poor diversity at any finite rate, the MMSE
receiver error curve slope flattens out progressively, as the coding rate
increases.
When SNR is fixed and the number of antennas becomes large, we show that the
mutual information at the output of a MMSE or ZF linear receiver has
fluctuations that converge in distribution to a Gaussian random variable, whose
mean and variance can be characterized in closed form. This analysis extends to
the linear receiver case a well-known result previously obtained for the
optimal receiver. Simulations reveal that the asymptotic analysis captures
accurately the outage behavior of systems even with a moderate number of
antennas.Comment: 48 pages, Submitted to IEEE Transactions on Information Theor
Performance of MMSE MIMO Receivers: A Large N Analysis for Correlated Channels
Linear receivers are considered as an attractive low-complexity alternative
to optimal processing for multi-antenna MIMO communications. In this paper we
characterize the performance of MMSE MIMO receivers in the limit of large
antenna numbers in the presence of channel correlations. Using the replica
method, we generalize our results obtained in arXiv:0810.0883 to
Kronecker-product correlated channels and calculate the asymptotic mean and
variance of the mutual information of a MIMO system of parallel MMSE
subchannels. The replica method allows us to use the ties between the optimal
receiver mutual information and the MMSE SIR of Gaussian inputs to calculate
the joint moments of the SIRs of the MMSE subchannels. Using the methodology
discussed in arXiv:0810.0883 it can be shown that the mutual information
converges in distribution to a Gaussian random variable. Our results agree very
well with simulations even with a moderate number of antennas.Comment: Invited article at the IEEE Vehicular Technology Conference,
Barcelona 200
The effect of a light radion on the triviality bound on higgs mass
In this paper we study how the triviality bound on higgs mass in the context
of the SM is modified by a light stabilized radion of the Goldberger-Wise
variety. Our approach is inherently perturbative. Including the radion
contribution to \bt(\l) and \bt(g_t) to one loop we evolve the higgs self
coupling \l from the cut off \L(=\vphi) down to the EW scale .
The triviality bound is obtained by requiring that \l(\L) = \sqrt{4 \pi}
which is the perturbative limit. We also study the effect of small changes in
the UVBC on the triviality bound both in the presence and absence of a light
radion.Comment: 9 pages, latex, 2 eps figure
Raman Evidence for Superconducting Gap and Spin-Phonon Coupling in Superconductor Ca(Fe0.95Co0.05)2As2
Inelastic light scattering studies on single crystal of electron-doped
Ca(Fe0.95Co0.05)2As2 superconductor, covering the tetragonal to orthorhombic
structural transition as well as magnetic transition at TSM ~ 140 K and
superconducting transition temperature Tc ~ 23 K, reveal evidence for
superconductivity-induced phonon renormalization; in particular the phonon mode
near 260 cm-1 shows hardening below Tc, signaling its coupling with the
superconducting gap. All the three Raman active phonon modes show anomalous
temperature dependence between room temperature and Tc i.e phonon frequency
decreases with lowering temperature. Further, frequency of one of the modes
shows a sudden change in temperature dependence at TSM. Using first-principles
density functional theory-based calculations, we show that the low temperature
phase (Tc < T < TSM) exhibits short-ranged stripe anti-ferromagnetic ordering,
and estimate the spin-phonon couplings that are responsible for these phonon
anomalies
Identifying new physics contributions in the Higgs sector at linear e+e- colliders
Loop driven decay modes of the Higgs are sensitive to new physics
contributions because of new particles in the loops. To highlight this we look
at the dilepton-dijet signal in the dominant Higgs production channel at a
linear e+e- collider. We show that by taking a simple ratio between
cross-sections of two different final states such contributions can be very
easily identified.Comment: Latex 4 pages, 2 eps figures (style files included). Talk given at
the linear collider workshop LCWS06, Bangalore, March 200
Long-range and short-range magnetic correlations, and microscopic origin of net magnetization in the spin-1 trimer chain compound CaNi3P4O14
Spin-spin correlations and microscopic origin of net magnetization in the
spin-1 trimer chain compound CaNi3P4O14 have been investigated by powder
neutron diffraction. The present study reveals a 3D long-range magnetic
ordering below 16 K where the magnetic structure consists of ferromagnetic
trimers that are coupled ferromagnetically along the spin-chain. The moment
components along the a and c axes arrange antiferromagnetically. Our study
establishes that the uncompensated moment components along the b axis result in
a net magnetization per unit cell. The magnetic structure, determined in the
present study, is in agreement with the results of recent first principles
calculation; however, it is in contrast to a fascinating experimental
prediction of ferrimagnetic ordering based on the periodicity of the exchange
interactions in CaNi3P4O14. Our study also confirms the presence of broad
diffuse magnetic scattering, due to 1D short-range spin-spin correlations, over
a wide temperature range below ~50 K down to a temperature well below the Tc.
Total neutron scattering analysis by the RMC method reveals that the dominating
spin-spin correlation above Tc is ferromagnetic and along the b axis. The
nearest neighbour spin-spin correlations along the a and c axes are found to be
weakly antiferromagnetic. The nature of the trimer spin structure of the
short-range state is similar to that of the 3D long-range ordered state. The
present investigation of microscopic nature of the magnetic ground state also
explains the condition required for the 1/3 magnetization plateau to be
observed in the trimer spin-chains. In spite of the S=1 trimer chain system,
the present compound CaNi3P4O14 is found to be a good realization of 3D magnet
below the Tc=16 K with full ordered moment values of ~2 mu_B/Ni2+ (1.98 and
1.96 mu_B/Ni2+ for two Ni sites, respectively) at 1.5 K.Comment: 10 pages, 8 figure
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