92 research outputs found
Taking advantage of multiplet structure for lineshape analysis in Fourier space
Lineshape analysis is a recurrent and often computationally intensive task in
optics, even more so for multiple peaks in the presence of noise. We
demonstrate an algorithm which takes advantage of peak multiplicity (N) to
retrieve line shape information. The method is exemplified via analysis of
Lorentzian and Gaussian contributions to individual lineshapes for a practical
spectroscopic measurement and benefits from a linear increase in sensitivity
with the number N. The robustness of the method and its benefits in terms of
noise reduction and order of magnitude improvement in run-time performance are
discussed.Comment: 12 pages, 6 figure
Direct and alignment-insensitive measurement of cantilever curvature
We analytically derive and experimentally demonstrate a method for the
simultaneous measurement of deflection for large arrays of cantilevers. The
Fresnel diffraction patterns of a cantilever independently reveals tilt,
curvature, cubic and higher order bending of the cantilever. It provides a
calibrated absolute measurement of the polynomial coefficients describing the
cantilever shape, without careful alignment and could be applied to several
cantilevers simultaneously with no added complexity. We show that the method is
easily implemented, works in both liquid mediums and in air, for a broad range
of displacements and is especially suited to the requirements for multi-marker
biosensors.Comment: 5 Pages, 4 figures, letter forma
Optical diffraction for measurements of nano-mechanical bending
Micromechanical transducers such as cantilevers for AFM often rely on optical
readout methods that require illumination of a specific region of the
microstructure. Here we explore and exploit the diffraction effects that have
been previously neglected when modeling cantilever bending measurement
techniques. The illumination of a cantilever end causes an asymmetric
diffraction pattern at the photodetector that significantly affects the
calibration of the signal in the popular optical beam deflection technique
(OBDT). Conditions for optimized linear signals that avoid detection artifacts
conflict with small numerical aperture illumination and narrow cantilevers
which are softer and therefore more sensitive. Embracing diffraction patterns
as a physical measurable allows a richer detection technique that decouples
measurements of tilt and curvature and simultaneously relaxes the requirements
on the alignment of illumination and detector. We show analytical results,
numerical simulations and physiologically relevant experimental data
demonstrating the usefulness of these diffraction features. We offer
experimental design guidelines and identify and quantify possible sources of
systematic error of up to 10% in OBDT. We demonstrate a new nanometre
resolution detection method that can replace OBDT, where Frauenhofer and Bragg
diffraction effects from finite sized and patterned cantilevers are exploited.
Such effects are readily generalized to arrays, and allow transmission
detection of mechanical curvature, enabling in-line instruments. In particular,
a cantilever with a periodic array of slots produces Bragg peaks which can be
analyzed to deduce the cantilever curvature. We highlight the comparative
advantages over OBDT by detecting molecular activity of antibiotic Vancomycin,
with an RMS noise equivalent to less than (1.5 nm), as example of
possible multi-maker bio-assays.Comment: 9 pages, 8 figure
Using random testing to manage a safe exit from the COVID-19 lockdown
We argue that frequent sampling of the fraction of infected people (either by
random testing or by analysis of sewage water), is central to managing the
COVID-19 pandemic because it both measures in real time the key variable
controlled by restrictive measures, and anticipates the load on the healthcare
system due to progression of the disease. Knowledge of random testing outcomes
will (i) significantly improve the predictability of the pandemic, (ii) allow
informed and optimized decisions on how to modify restrictive measures, with
much shorter delay times than the present ones, and (iii) enable the real-time
assessment of the efficiency of new means to reduce transmission rates.
Here we suggest, irrespective of the size of a suitably homogeneous
population, a conservative estimate of 15000 for the number of randomly tested
people per day which will suffice to obtain reliable data about the current
fraction of infections and its evolution in time, thus enabling close to
real-time assessment of the quantitative effect of restrictive measures. Still
higher testing capacity permits detection of geographical differences in
spreading rates. Furthermore and most importantly, with daily sampling in
place, a reboot could be attempted while the fraction of infected people is
still an order of magnitude higher than the level required for a relaxation of
restrictions with testing focused on symptomatic individuals. This is
demonstrated by considering a feedback and control model of mitigation where
the feed-back is derived from noisy sampling data.Comment: 18 pages, 6 figures, 2 appendices. Phys. Biol. (2020
High-Frequency Spin Waves in YBaâCuâO\u3csub\u3e6.15\u3e/sub\u3e
Pulsed neutron spectroscopy is used to absolute measurements of the dynamic magnetic susceptibility of insulating YBa2Cu3O6.15. Acoustic and optical modes, derived from inand out-of-phase oscillation of spins in adjacent CuO2 planes, dominate the spectra and are observed up to 250 meV. The optical modes appear first at 74±5 meV. Linear-spin-wave theory gives an excellent description of the data and yields intralayer and interlayer exchange constants of J∥=125±5 meV and Jâ„=11±2 meV, respectively, and a spin-wave intensity renormalization ZΧ=0.4±0.1
Influence of oxygen pressure and aging on LaAlO3 films grown by pulsed laser deposition on SrTiO3 substrates
The crystal structures of LaAlO3 films grown by pulsed laser deposition on
SrTiO3 substrates at oxygen pressure of 10-3 mbar or 10-5 mbar, where kinetics
of ablated species hardly depend on oxygen background pressure, are compared.
Our results show that the interface between LaAlO3 and SrTiO3 is sharper when
the oxygen pressure is lower. Over time, the formation of various crystalline
phases is observed while the crystalline thickness of the LaAlO3 layer remains
unchanged. X-ray scattering as well as atomic force microscopy measurements
indicate three-dimensional growth of such phases, which appear to be fed from
an amorphous capping layer present in as-grown samples
Quantum phase transitions in transverse field spin models: from statistical physics to quantum information
We review quantum phase transitions of spin systems in transverse magnetic
fields taking the examples of the spin-1/2 Ising and XY models in a transverse
field. Beginning with an overview of quantum phase transitions, we introduce a
number of model Hamiltonians. We provide exact solutions in one spatial
dimension connecting them to conformal field theoretical studies. We also
discuss Kitaev models and some other exactly solvable spin systems. Studies of
quantum phase transitions in the presence of quenched randomness and with
frustrating interactions are presented in detail. We discuss novel phenomena
like Griffiths-McCoy singularities. We then turn to more recent topics like
information theoretic measures of the quantum phase transitions in these models
such as concurrence, entanglement entropy, quantum discord and quantum
fidelity. We then focus on non-equilibrium dynamics of a variety of transverse
field systems across quantum critical points and lines. After mentioning rapid
quenching studies, we dwell on slow dynamics and discuss the Kibble-Zurek
scaling for the defect density following a quench across critical points and
its modifications for quenching across critical lines, gapless regions and
multicritical points. Topics like the role of different quenching schemes,
local quenching, quenching of models with random interactions and quenching of
a spin chain coupled to a heat bath are touched upon. The connection between
non-equilibrium dynamics and quantum information theoretic measures is
presented at some length. We indicate the connection between Kibble-Zurek
scaling and adiabatic evolution of a state as well as the application of
adiabatic dynamics as a tool of a quantum optimization technique known as
quantum annealing. The final section is dedicated to a detailed discussion on
recent experimental studies of transverse Ising-like systems.Comment: 106 pages, 38 figures; an expanded version has been published as a
book (330 pages, 72 figures, 874 references) as A. Dutta, G. Aeppli, B. K.
Chakrabarti, U. Divakaran, T. F. Rosenbaum and D. Sen, Quantum Phase
Transitions in Transverse Field Spin Models: From Statistical Physics to
Quantum Information (Cambridge University Press, Cambridge, 2015
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