451 research outputs found
Reduction of Quantum Noise in Transmittance Estimation Using PhotoneCorrelated Beams
The accuracy of optical measurements at low light levels is limited by the quantum noise of the source and by the random nature of the interaction with the measured object. The source noise may be reduced by use of nonclassical photon-number squeezed light. This paper considers the use of two photon-correlated beams (generated, for example, by spontaneous parametric downconversion) to measure the optical transmittance of an object. The photons of each beam obey a random Poisson process, but are synchronized in time. One beam is used to probe the object while the other is used as a reference providing information on the realization of the random arrival of photons at the object. The additional information available by such measurement may be exploited to improve the accuracy of the measurement. Various estimators, including the maximum likelihood estimator, are considered and their performance is evaluated and compared with the measurement based on single-beam conventional (Poisson) source and maximally squeezed (fixed photon number) source. The performance advantage established in this paper depends on parameters such as the intensity of the source, the transmittance of the object, the quantum efficiency of the detectors, the background noise, and the degree of correlation of the photon numbers in the two beams
Aberration cancellation in quantum interferometry
We report the first experimental demonstration of even-order aberration
cancellation in quantum interferometry. The effect is a spatial counterpart of
the spectral group velocity dispersion cancellation, which is associated with
spectral entanglement. It is manifested in temporal interferometry by virtue of
the multi-parameter spatial-spectral entanglement. Spatially-entangled photons,
generated by spontaneous parametric down conversion, were subjected to spatial
aberrations introduced by a deformable mirror that modulates the wavefront. We
show that only odd-order spatial aberrations affect the quality of quantum
interference
Performance of privatised and private firms : empirical evidence from Egypt
Privatisation has been a major political and economic phenomenon over the
past few decades, and researchers continue to target it for both theoretical and
empirical work.
The objective of this thesis is to evaluate the Egyptian experiment concerning
its privatisation programme, and to determine whether this programme has
affected the performance of privatised firms. Using 15 years of data, which
cover the period 1990/1991 to 2004/2005; this thesis empirically investigates
three main issues. Firstly, it examines whether the performance of privatised
firms improves following privatisation through comparing pre- and postprivatisation
performance in terms of profitability, operating efficiency, output,
leverage and level of employment. Secondly, it evaluates the performance
changes of privatised Egyptian firms after matching them to control firms
(private firms) based on size and industry. Thirdly, it evaluates the impact of the
post-privatisation sectoral environment and the pre-privatisation experience on
post-privatisation performance.
For the first two issues, several statistical techniques, such as parametric t-test,
the non-parametric Wilcoxon signed-rank test, and Mann-Whitney test are
performed. The results from this analysis indicate clearly that there are
significant increases in both profitability and operating efficiency as well as
significant declines in the leverage and employment, but there is no significant
change in the output. Furthermore, the results show a significant difference in
performance changes between privatised firms and private firms according to
most performance measures.
As to the third issue, several multi-regressions are used to model the
relationship between the post-privatisation performance (as dependent variable)
and ownership structure, the performance experience of the privatised firms
pre-privatisation, the performance of their counterparts from competitor firms
(private firms), and firm size (as independent variables). The results from this
analysis demonstrate that the ownership structure really matters and that the
performance of privatised firms depends on the degree of state ownership
involvement; also, through the passage of time, the competitive environment
has a significant impact on most performance measures of privatised firms.
As such, this thesis represents the first study in Egypt to evaluate and compare
the performance of privatised firms with the performance of their counterparts
from private firms. The study contributes to the work on privatisation by
comparing the performance changes of privatised firms to those of already
private ones, so that the study can determine whether the post-privatisation
performance matches that of the private firms.
A caveat to the finding of this thesis is that the privatised firms might need a
longer period to reflect more fully the impact of the privatisation programme on
some of their performance measures.Arab Academy for
Science and Technology, Egyp
Synthesis and Analysis of Entangled Photonic Qubits in Spatial-Parity Space
We present the novel embodiment of a photonic qubit that makes use of one
continuous spatial degree of freedom of a single photon and relies on the the
parity of the photon's transverse spatial distribution. Using optical
spontaneous parametric downconversion to produce photon pairs, we demonstrate
the controlled generation of entangled-photon states in this new space.
Specifically, two Bell states, and a continuum of their superpositions, are
generated by simple manipulation of a classical parameter, the optical-pump
spatial parity, and not by manipulation of the entangled photons themselves. An
interferometric device, isomorphic in action to a polarizing beam splitter,
projects the spatial-parity states onto an even--odd basis. This new physical
realization of photonic qubits could be used as a foundation for future
experiments in quantum information processing.Comment: 6 pages, 5 figures, submitted to PR
Optimum conditions for Inulinase production by Aspergillus niger using solid state fermentation
Thirty local fungal isolates according to Aspergillus niger were screened for Inulinase production on synthetic solid medium depending on inulin hydrolysis appear as clear zone around fungal colony. Semi-quantitative screening was performed to select the most efficient isolate for inulinase production. the most efficient isolate was AN20. The optimum condition for enzyme production from A. niger isolate was determined by busing a medium composed of sugar cane moisten with corn steep liquor 5;5 (v/w) at initial pH 5.0 for 96 hours at 30 0C . Enzyme productivity was tested for each of the yeast Kluyveromyces marxianus, the fungus A. niger AN20 and for a mixed culture of A. niger and K. marxianus. The productivity of A. niger gave the highest specific activity of 153 U/mg, as compared with K. marxianus which gave 86 U/mg
Impact-ionization and noise characteristics of thin III-V avalanche photodiodes
It is, by now, well known that McIntyre\u27s localized carrier-multiplication theory cannot explain the suppression of excess noise factor observed in avalanche photodiodes (APDs) that make use of thin multiplication regions. We demonstrate that a carrier multiplication model that incorporates the effects of dead space, as developed earlier by Hayat et al. provides excellent agreement with the impact-ionization and noise characteristics of thin InP, In/sub 0.52/Al/sub 0.48/As, GaAs, and Al/sub 0.2/Ga/sub 0.8/As APDs, with multiplication regions of different widths. We outline a general technique that facilitates the calculation of ionization coefficients for carriers that have traveled a distance exceeding the dead space (enabled carriers), directly from experimental excess-noise-factor data. These coefficients depend on the electric field in exponential fashion and are independent of multiplication width, as expected on physical grounds. The procedure for obtaining the ionization coefficients is used in conjunction with the dead-space-multiplication theory (DSMT) to predict excess noise factor versus mean-gain curves that are in excellent accord with experimental data for thin III-V APDs, for all multiplication-region widths
Speed Control of Hydraulic Elevator by Using Electro-Hydraulic Servo Mechanism
المصعد الهيدروليكي هو أحد أنواع المصاعد المستخدمة في المباني ذات الارتفاع المنخفض والذي لا يزيد عن الثلاث طوابق. في هذا البحث تم نصب وتنفيذ وتشغيل نموذج مصغر لمصعد هيدروليكي والتحقق النظري والتجريبي باستخدام صمام تناسبي، ومسيطر نوع PI. تم تنفيذ المصعد مع ثلاث طوابق بارتفاع كلي يبلغ 76 سم مع جميع المكونات والملحقات الهيدروليكية والكهربائية، حيث ان اتمتة المصعد كانت باستخدام مايكرو كونترولر اردوينو ِArduino نوع أونو. UNO
برنامج الحاسوب اللابفيو LABVEIW تم استخدامه للسيطرة على المصعد من خلال مسوق التيار المستمر L298 DC.
أفضل قيم لباراميترات المسيطر PI تم الحصول عليها تجريبيا.
النتائج أظهرت دعم وتحسين الأداء للمصعد الهيدروليكي من خلال استخدام نظام المؤازرة الكهروهيدروليكي لتحقيق التوقف السلس وراحة المستخدمين للمصعد في التنقل بحركة انسيابية بين الطوابق.An electro-hydraulic elevator is a new type of enhanced elevators used in low-rise buildings, no more than eight floors. In this paper, an electro-hydraulic servo system for controlling the speed of a hydraulic elevator prototype by using a proportional valve and PI controller has been investigated theoretically and experimentally. A three floors elevator prototype model with 76cm height has been built, including hydraulic components and electrical components. The elevator system is automated using an Arduino UNO board based Data Acquisition (DAQ) system. LabVIEW software is programmed to control the hydraulic elevator system through L298 DC drive via the DAQ board. The best PI gains have been calculated experimentally using Ziegler–Nichols, trial and error methods. The results showed the effectiveness of the use of Electro-hydraulic servomechanism in enhancing the performance of the hydraulic elevator in terms of comfort and smoothness when people travelled through the elevator floors
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