504 research outputs found
In Vitro Formation of Urinary Stones : Generation of Spherulites of Calcium Phosphate in Gel and Overgrowth with Calcium Oxalate Using a New Flow Model of Crystallization
Calcium phosphate (CaP) has been detected in the majority of urinary stones containing predominantly calcium oxalate (CaOx). Therefore, crystal phases of CaP might play an important role with respect to the formation of urinary calcium stones in general. Very often, CaP found in stones or tissue of human kidney occurs in the shape of small spherulites. In this paper, we report on a new flow model of crystallization (FMCG), which has been used to generate spherulites of CaP in a gel matrix of 1% agar-agar at 37°C from a supersaturated, metastable solution continuously flowing over the gel surface. Scanning electron microscopy (SEM), X-ray diffraction and microscopic Fourier transformed infrared spectroscopy (FTIR) revealed that the particles formed (diameter: up to 200 μm) consisted of a poorly crystal-line core of carbonatoapatite which was partly surrounded by a well-crystallized shell of octacalcium phosphate (OCP) showing radially oriented sheet-like structures. Subsequently, CaOx was grown on these spherulites from a flow of a correspondingly supersaturated solution conducted over the gel matrix. It could be shown by SEM that growth of calcium oxalate monohydrate (COM) was characteristically induced by the OCP shell. Radial sheet-like forms of OCP were directly continued by COM showing a certain radial orientation.
The model of crystallization in gel matrices applied here should be well-suited to simulate the process of urinary stone formation under in vitro conditions
Fast quantum key distribution with decoy number states
We investigate the use of photon number states to identify eavesdropping
attacks on quantum key distribution (QKD) schemes. The technique is based on
the fact that different photon numbers traverse a channel with different
transmittivity. We then describe two QKD schemes that utilize this method, one
of which overcomes the upper limit on the key generation rate imposed by the
dead time of detectors when using a heralded source of photons.Comment: 15 pages, 6 figures; Accepted to J. Mod. Op
Experimental joint signal-idler quasi-distributions and photon-number statistics for mesoscopic twin beams
Joint signal-idler photoelectron distributions of twin beams containing
several tens of photons per mode have been measured recently. Exploiting a
microscopic quantum theory for joint quasi-distributions in parametric
down-conversion developed earlier we characterize properties of twin beams in
terms of quasi-distributions using experimental data. Negative values as well
as oscillating behaviour in quantum region are characteristic for the
subsequently determined joint signal-idler quasi-distributions of integrated
intensities. Also the conditional and difference photon-number distributions
are shown to be sub-Poissonian and sub-shot-noise, respectively.Comment: 7 pages, 6 figure
From Linear Optical Quantum Computing to Heisenberg-Limited Interferometry
The working principles of linear optical quantum computing are based on
photodetection, namely, projective measurements. The use of photodetection can
provide efficient nonlinear interactions between photons at the single-photon
level, which is technically problematic otherwise. We report an application of
such a technique to prepare quantum correlations as an important resource for
Heisenberg-limited optical interferometry, where the sensitivity of phase
measurements can be improved beyond the usual shot-noise limit. Furthermore,
using such nonlinearities, optical quantum nondemolition measurements can now
be carried out at the single-photon level.Comment: 10 pages, 5 figures; Submitted to a Special Issue of J. Opt. B on
"Fluctuations and Noise in Photonics and Quantum Optics" (Herman Haus
Memorial Issue); v2: minor change
Measuring measurement
Measurement connects the world of quantum phenomena to the world of classical
events. It plays both a passive role, observing quantum systems, and an active
one, preparing quantum states and controlling them. Surprisingly - in the light
of the central status of measurement in quantum mechanics - there is no general
recipe for designing a detector that measures a given observable. Compounding
this, the characterization of existing detectors is typically based on partial
calibrations or elaborate models. Thus, experimental specification (i.e.
tomography) of a detector is of fundamental and practical importance. Here, we
present the realization of quantum detector tomography: we identify the optimal
positive-operator-valued measure describing the detector, with no ancillary
assumptions. This result completes the triad, state, process, and detector
tomography, required to fully specify an experiment. We characterize an
avalanche photodiode and a photon number resolving detector capable of
detecting up to eight photons. This creates a new set of tools for accurately
detecting and preparing non-classical light.Comment: 6 pages, 4 figures,see video abstract at
http://www.quantiki.org/video_abstracts/0807244
Photon-number distributions of twin beams generated in spontaneous parametric down-conversion and measured by an intensified CCD camera
The measurement of photon-number statistics of fields composed of photon
pairs, generated in spontaneous parametric down-conversion and detected by an
intensified CCD camera is described. Final quantum detection efficiencies,
electronic noises, finite numbers of detector pixels, transverse intensity
spatial profiles of the detected beams as well as losses of single photons from
a pair are taken into account in a developed general theory of photon-number
detection. The measured data provided by an iCCD camera with single-photon
detection sensitivity are analyzed along the developed theory. Joint
signal-idler photon-number distributions are recovered using the reconstruction
method based on the principle of maximum likelihood. The range of applicability
of the method is discussed. The reconstructed joint signal-idler photon-number
distribution is compared with that obtained by a method that uses superposition
of signal and noise and minimizes photoelectron entropy. Statistics of the
reconstructed fields are identified to be multi-mode Gaussian. Elements of the
measured as well as the reconstructed joint signal-idler photon-number
distributions violate classical inequalities. Sub-shot-noise correlations in
the difference of the signal and idler photon numbers as well as partial
suppression of odd elements in the distribution of the sum of signal and idler
photon numbers are observed.Comment: 14 pages, 14 figure
Determinants and implications of the growing scale of livestock farms in four fast-growing developing countries:
"The rapid growth in consumer demand for livestock offers an opportunity to reduce poverty among smallholder livestock farmers in the developing world. These farmers' opportunity may be threatened, however, by competition from larger-scale farms. This report assesses the potential threat, examining various forms of livestock production in Brazil, India, the Philippines, and Thailand. Findings show that the competitiveness of smallholder farms depends on the opportunity cost of family labor and farmers' ability to overcome barriers to the acquisition of production- and market-related information and assets. Pro-poor livestock development depends, therefore, on the strengthening of institutions that will help smallholders overcome the disproportionately high transaction costs in securing quality inputs and obtaining market recognition for quality outputs. These and other findings make this report a useful guide for researchers and others concerned with the opportunities and risks of smallholder livestock farming." from Authors' SummaryDeveloping countries, Economic aspects, Industrialization, Profit efficiency, Environmental externalities, Smallholder competitiveness, Livestock productivity, Livestock Industrialization, Scaling up,
An avalanche-photodiode-based photon-number-resolving detector
Avalanche photodiodes are widely used as practical detectors of single
photons.1 Although conventional devices respond to one or more photons, they
cannot resolve the number in the incident pulse or short time interval.
However, such photon number resolving detectors are urgently needed for
applications in quantum computing,2-4 communications5 and interferometry,6 as
well as for extending the applicability of quantum detection generally. Here we
show that, contrary to current belief,3,4 avalanche photodiodes are capable of
detecting photon number, using a technique to measure very weak avalanches at
the early stage of their development. Under such conditions the output signal
from the avalanche photodiode is proportional to the number of photons in the
incident pulse. As a compact, mass-manufactured device, operating without
cryogens and at telecom wavelengths, it offers a practical solution for photon
number detection.Comment: 12 pages, 4 figure
Cryotolerance and pregnancy rates after exposure of bovine in vitro-produced embryos to forskolin and linoleic acid before vitrification.
The objective of the present study was to evaluate the effects of supplementation of in vitro culture (IVC) medium with drugs that stimulates the lipolysis (Forskolin: Forsk) and inhibit the lipogenesis (Linoleic Acid LA) on the intracytoplasmic lipid content and cryotolerance of bovine embryos (Experiment 1), as well as to evaluate the effect of treatment of embryos with Forsk on the pregnancy rates after transfer to synchronized recipients (Experiment 2).Proceedings of the 30th Annual Meeting of the Brazilian Embryo Technology Society (SBTE); Foz do Iguaçu, PR, Brazil, August 25th to 27th, 2016, and 32nd Meeting of the European Embryo Transfer Association (AETE); Barcelona, Spain, September 9th and 10th, 2016. A327 Support Biotechnologies: Cryopreservation and cryobiology, diagnosis through imaging, molecular biology and ?omics?. Título em português: Criotolerância e taxa de concepção após exposição de embriões bovinos produzidos in vitro ao Forskolin ou ácido linoleico antes da vitrificação
Avalanche Photo-Detection for High Data Rate Applications
Avalanche photo detection is commonly used in applications which require
single photon sensitivity. We examine the limits of using avalanche photo
diodes (APD) for characterising photon statistics at high data rates. To
identify the regime of linear APD operation we employ a ps-pulsed diode laser
with variable repetition rates between 0.5MHz and 80MHz. We modify the mean
optical power of the coherent pulses by applying different levels of
well-calibrated attenuation. The linearity at high repetition rates is limited
by the APD dead time and a non-linear response arises at higher photon-numbers
due to multiphoton events. Assuming Poissonian input light statistics we
ascertain the effective mean photon-number of the incident light with high
accuracy. Time multiplexed detectors (TMD) allow to accomplish photon- number
resolution by photon chopping. This detection setup extends the linear response
function to higher photon-numbers and statistical methods may be used to
compensate for non-linearity. We investigated this effect, compare it to the
single APD case and show the validity of the convolution treatment in the TMD
data analysis.Comment: 16 pages, 5 figure
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