55,463 research outputs found
Shot noise limited characterization of femtosecond light pulses
Probing the evolution of physical systems at the femto- or attosecond
timescale with light requires accurate characterization of ultrashort optical
pulses. The time profiles of such pulses are usually retrieved by methods
utilizing optical nonlinearities, which require significant signal powers and
operate in a limited spectral
range\cite{Trebino_Review_of_Scientific_Instruments97,Walmsley_Review_09}. We
present a linear self-referencing characterization technique based on time
domain localization of the pulse spectral components, operated in the
single-photon regime. Accurate timing of the spectral slices is achieved with
standard single photon detectors, rendering the technique applicable in any
spectral range from near infrared to deep UV. Using detection electronics with
about ps response, we retrieve the temporal profile of a picowatt pulse
train with fs resolution, setting a new scale of sensitivity in
ultrashort pulse characterization.Comment: Supplementary information contained in raw dat
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Time-frequency representation of earthquake accelerograms and inelastic structural response records using the adaptive chirplet decomposition and empirical mode decomposition
In this paper, the adaptive chirplet decomposition combined with the Wigner-Ville transform and the empirical mode decomposition combined with the Hilbert transform are employed to process various non-stationary signals (strong ground motions and structural responses). The efficacy of these two adaptive techniques for capturing the temporal evolution of the frequency content of specific seismic signals is assessed. In this respect, two near-field and two far-field seismic accelerograms are analyzed. Further, a similar analysis is performed for records pertaining to the response of a 20-story steel frame benchmark building excited by one of the four accelerograms scaled by appropriate factors to simulate undamaged and severely damaged conditions for the structure. It is shown that the derived joint time–frequency representations of the response time histories capture quite effectively the influence of non-linearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event; in this context, tracing the mean instantaneous frequency of records of critical structural responses is adopted.
The study suggests, overall, that the aforementioned techniques are quite viable tools for detecting and monitoring damage to constructed facilities exposed to seismic excitations
Spherical harmonic transform with GPUs
We describe an algorithm for computing an inverse spherical harmonic
transform suitable for graphic processing units (GPU). We use CUDA and base our
implementation on a Fortran90 routine included in a publicly available parallel
package, S2HAT. We focus our attention on the two major sequential steps
involved in the transforms computation, retaining the efficient parallel
framework of the original code. We detail optimization techniques used to
enhance the performance of the CUDA-based code and contrast them with those
implemented in the Fortran90 version. We also present performance comparisons
of a single CPU plus GPU unit with the S2HAT code running on either a single or
4 processors. In particular we find that use of the latest generation of GPUs,
such as NVIDIA GF100 (Fermi), can accelerate the spherical harmonic transforms
by as much as 18 times with respect to S2HAT executed on one core, and by as
much as 5.5 with respect to S2HAT on 4 cores, with the overall performance
being limited by the Fast Fourier transforms. The work presented here has been
performed in the context of the Cosmic Microwave Background simulations and
analysis. However, we expect that the developed software will be of more
general interest and applicability
Print-Scan Resilient Text Image Watermarking Based on Stroke Direction Modulation for Chinese Document Authentication
Print-scan resilient watermarking has emerged as an attractive way for document security. This paper proposes an stroke direction modulation technique for watermarking in Chinese text images. The watermark produced by the idea offers robustness to print-photocopy-scan, yet provides relatively high embedding capacity without losing the transparency. During the embedding phase, the angle of rotatable strokes are quantized to embed the bits. This requires several stages of preprocessing, including stroke generation, junction searching, rotatable stroke decision and character partition. Moreover, shuffling is applied to equalize the uneven embedding capacity. For the data detection, denoising and deskewing mechanisms are used to compensate for the distortions induced by hardcopy. Experimental results show that our technique attains high detection accuracy against distortions resulting from print-scan operations, good quality photocopies and benign attacks in accord with the future goal of soft authentication
Quantum-dot based photonic quantum networks
Quantum dots embedded in photonic nanostructures have in recent years proven
to be a very powerful solid-state platform for quantum optics experiments. The
combination of near-unity radiative coupling of a single quantum dot to a
photonic mode and the ability to eliminate decoherence processes imply that an
unprecedented light-matter interface can be obtained. As a result,
high-cooperativity photon-emitter quantum interfaces can be constructed opening
a path-way to deterministic photonic quantum gates for quantum-information
processing applications. In the present manuscript, I review current
state-of-the-art on quantum dot devices and their applications for quantum
technology. The overarching long-term goal of the research field is to
construct photonic quantum networks where remote entanglement can be
distributed over long distances by photons
Data-driven Job Search Engine Using Skills and Company Attribute Filters
According to a report online, more than 200 million unique users search for
jobs online every month. This incredibly large and fast growing demand has
enticed software giants such as Google and Facebook to enter this space, which
was previously dominated by companies such as LinkedIn, Indeed and
CareerBuilder. Recently, Google released their "AI-powered Jobs Search Engine",
"Google For Jobs" while Facebook released "Facebook Jobs" within their
platform. These current job search engines and platforms allow users to search
for jobs based on general narrow filters such as job title, date posted,
experience level, company and salary. However, they have severely limited
filters relating to skill sets such as C++, Python, and Java and company
related attributes such as employee size, revenue, technographics and
micro-industries. These specialized filters can help applicants and companies
connect at a very personalized, relevant and deeper level. In this paper we
present a framework that provides an end-to-end "Data-driven Jobs Search
Engine". In addition, users can also receive potential contacts of recruiters
and senior positions for connection and networking opportunities. The high
level implementation of the framework is described as follows: 1) Collect job
postings data in the United States, 2) Extract meaningful tokens from the
postings data using ETL pipelines, 3) Normalize the data set to link company
names to their specific company websites, 4) Extract and ranking the skill
sets, 5) Link the company names and websites to their respective company level
attributes with the EVERSTRING Company API, 6) Run user-specific search queries
on the database to identify relevant job postings and 7) Rank the job search
results. This framework offers a highly customizable and highly targeted search
experience for end users.Comment: 8 pages, 10 figures, ICDM 201
Subradiant states of quantum bits coupled to a one-dimensional waveguide
The properties of coupled emitters can differ dramatically from those of
their individual constituents. Canonical examples include sub- and
super-radiance, wherein the decay rate of a collective excitation is reduced or
enhanced due to correlated interactions with the environment. Here, we
systematically study the properties of collective excitations for regularly
spaced arrays of quantum emitters coupled to a one-dimensional (1D) waveguide.
We find that, for low excitation numbers, the modal properties are
well-characterized by spin waves with a definite wavevector. Moreover, the
decay rate of the most subradiant modes obeys a universal scaling with a cubic
suppression in the number of emitters. Multi-excitation subradiant eigenstates
can be built from fermionic combinations of single excitation eigenstates; such
"fermionization" results in multiple excitations that spatially repel one
another. We put forward a method to efficiently create and measure such
subradiant states, which can be realized with superconducting qubits. These
measurement protocols probe both real-space correlations (using on-site
dispersive readout) and temporal correlations in the emitted field (using
photon correlation techniques).Comment: 21 pages, 9 figure
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