13,021 research outputs found
Ion beam induced enhanced diffusion from gold thin films in silicon
Enhanced diffusion of gold atoms into silicon substrate has been studied in
Au thin films of various thicknesses (2.0, 5.3, 10.9 and 27.5 nm) deposited on
Si(111) and followed by irradiation with 1.5 MeV Au2+ at a flux of 6.3x10^12
ions cm-2 s-1 and fluence up to 1x10^15 ions cm-2. The high resolution
transmission electron microscopy measurements showed the presence of gold
silicide formation for the above-mentioned systems at fluence greater than
equal to 1x1014 ions cm-2. The maximum depth to which the gold atoms have been
diffused at a fluence of 1x10^14 ions cm-2 for the cases of 2.0, 5.3, 10.9 and
27.5 nm thick films has been found to be 60, 95, 160 and 13 nm respectively.
Interestingly, at higher fluence of 1x1015 ions cm-2 in case of 27.5 nm thick
film, gold atoms from the film transported to a maximum depth of 265 nm in the
substrate. The substrate silicon is found to be amorphous at the above fluence
values where unusually large mass transport occurred. Enhanced diffusion has
been explained on the basis of ion beam induced, flux dependent amorphous
nature of the substrate, and transient beam induced temperature effects. This
work confirms the absence of confinement effects that arise from spatially
confined structures and existence of thermal and chemical reactions during ion
irradiation.Comment: 15 pages, 3 figure
Discriminating quantum-optical beam-splitter channels with number-diagonal signal states: Applications to quantum reading and target detection
We consider the problem of distinguishing, with minimum probability of error,
two optical beam-splitter channels with unequal complex-valued reflectivities
using general quantum probe states entangled over M signal and M' idler mode
pairs of which the signal modes are bounced off the beam splitter while the
idler modes are retained losslessly. We obtain a lower bound on the output
state fidelity valid for any pure input state. We define number-diagonal signal
(NDS) states to be input states whose density operator in the signal modes is
diagonal in the multimode number basis. For such input states, we derive series
formulas for the optimal error probability, the output state fidelity, and the
Chernoff-type upper bounds on the error probability. For the special cases of
quantum reading of a classical digital memory and target detection (for which
the reflectivities are real valued), we show that for a given input signal
photon probability distribution, the fidelity is minimized by the NDS states
with that distribution and that for a given average total signal energy N_s,
the fidelity is minimized by any multimode Fock state with N_s total signal
photons. For reading of an ideal memory, it is shown that Fock state inputs
minimize the Chernoff bound. For target detection under high-loss conditions, a
no-go result showing the lack of appreciable quantum advantage over coherent
state transmitters is derived. A comparison of the error probability
performance for quantum reading of number state and two-mode squeezed vacuum
state (or EPR state) transmitters relative to coherent state transmitters is
presented for various values of the reflectances. While the nonclassical states
in general perform better than the coherent state, the quantitative performance
gains differ depending on the values of the reflectances.Comment: 12 pages, 7 figures. This closely approximates the published version.
The major change from v2 is that Section IV has been re-organized, with a
no-go result for target detection under high loss conditions highlighted. The
last sentence of the abstract has been deleted to conform to the arXiv word
limit. Please see the PDF for the full abstrac
Phosphate mediated changes in phospholipids in Neurospora crassa.
Phosphate mediated changes in phospholipids in Neurospora crassa
Edges and Diffractive Effects in Casimir Energies
The prototypical Casimir effect arises when a scalar field is confined
between parallel Dirichlet boundaries. We study corrections to this when the
boundaries themselves have apertures and edges. We consider several geometries:
a single plate with a slit in it, perpendicular plates separated by a gap, and
two parallel plates, one of which has a long slit of large width, related to
the case of one plate being semi-infinite. We develop a general formalism for
studying such problems, based on the wavefunctional for the field in the gap
between the plates. This formalism leads to a lower dimensional theory defined
on the open regions of the plates or boundaries. The Casimir energy is then
given in terms of the determinant of the nonlocal differential operator which
defines the lower dimensional theory. We develop perturbative methods for
computing these determinants. Our results are in good agreement with known
results based on Monte Carlo simulations. The method is well suited to
isolating the diffractive contributions to the Casimir energy.Comment: 32 pages, LaTeX, 9 figures. v2: additional discussion of
renormalization procedure, version to appear in PRD. v3: corrected a sign
error in (70
Comparison between Windowed FFT and Hilbert-Huang Transform for Analyzing Time Series with Poissonian Fluctuations: A Case Study
Hilbert-Huang Transform (HHT) is a novel data analysis technique for
nonlinear and non-stationary data. We present a time-frequency analysis of both
simulated light curves and an X-ray burst from the X-ray burster 4U 1702-429
with both the HHT and the Windowed Fast Fourier Transform (WFFT) methods. Our
results show that the HHT method has failed in all cases for light curves with
Poissonian fluctuations which are typical for all photon counting instruments
used in astronomy, whereas the WFFT method can sensitively detect the periodic
signals in the presence of Poissonian fluctuations; the only drawback of the
WFFT method is that it cannot detect sharp frequency variations accurately.Comment: 10 pages, 12 figure
Asymptotic behavior of the least common multiple of consecutive arithmetic progression terms
Let and be two integers with , and let and be
integers with and . In this paper, we prove that , where is a constant depending on and .Comment: 8 pages. To appear in Archiv der Mathemati
Flux dependent 1.5 MeV self-ion beam induced sputtering from Gold nanostructured thin films
We discuss four important aspects of 1.5 MeV Au2+ ion-induced flux dependent
sputtering from gold nanostrcutures (of an average size 7.6 nm and height 6.9
nm) that are deposited on silicon substrates: (a) Au sputtering yield at the
ion flux of 6.3x10^12 ions cm-2 s-1 is found to be 312 atoms/ion which is about
five times the sputtering yield reported earlier under identical irradiation
conditions at a lower beam flux of 10^9 ions cm-2 s-1, (b) the sputtered yield
increases with increasing flux at lower fluence and reduces at higher fluence
(1.0x10^15 ions cm-2) for nanostructured thin films while the sputtering yield
increases with increasing flux and fluence for thick films (27.5 nm Au
deposited on Si) (c) Size distribution of sputtered particles has been found to
vary with the incident beam flux showing a bimodal distribution at higher flux
and (d) the decay exponent obtained from the size distributions of sputtered
particles showed an inverse power law dependence ranging from 1.5 to 2.5 as a
function of incident beam flux. The exponent values have been compared with
existing theoretical models to understand the underlying mechanism. The role of
wafer temperature associated with the beam flux has been invoked for a
qualitative understanding of the sputtering results in both the nanostructured
thin films and thick films.Comment: 25 pages, 5 figures, 1 table To be Appeared in J. Phys. D: Appl. Phy
Phosphate mediated changes in fatty acid composition in Neurospora crassa.
Phosphate mediated changes in fatty acid composition in Neurospora crassa
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