6,558 research outputs found
De Broglie Wavelength of a Nonlocal Four-Photon
Superposition is one of the most distinct features of quantum theory and has
been demonstrated in numerous realizations of Young's classical double-slit
interference experiment and its analogues. However, quantum entanglement - a
significant coherent superposition in multiparticle systems - yields phenomena
that are much richer and more interesting than anything that can be seen in a
one-particle system. Among them, one important type of multi-particle
experiments uses path-entangled number-states, which exhibit pure higher-order
interference and allow novel applications in metrology and imaging such as
quantum interferometry and spectroscopy with phase sensitivity at the
Heisenberg limit or quantum lithography beyond the classical diffraction limit.
Up to now, in optical implementations of such schemes lower-order interference
effects would always decrease the overall performance at higher particle
numbers. They have thus been limited to two photons. We overcome this
limitation and demonstrate a linear-optics-based four-photon interferometer.
Observation of a four-particle mode-entangled state is confirmed by
interference fringes with a periodicity of one quarter of the single-photon
wavelength. This scheme can readily be extended to arbitrary photon numbers and
thus represents an important step towards realizable applications with
entanglement-enhanced performance.Comment: 19 pages, 4 figures, submitted on November 18, 200
Normal saline resuscitation worsens lactic acidosis in experimental sepsis
It is well established that infusing large amounts of normal saline causes hyperchloremic acidosis, yet the clinical relevance of this is unknown.\ud
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We found that infusion of normal saline, compared with a balanced crystalloid, worsens lactic acidosis in experimental sepsis
Feed rate modeling in circular–circular interpolation discontinuity for high-speed milling
In this paper, a modeling approach is presented in order to evaluate feed rate during a circular interpolation in high-speed milling. The developed model depends on the type of discontinuity and the kinematic performance of the machine tool. To begin with, a feed rate modeling for circular interpolation with continuity in tangency is developed. After, the discontinuity in tangency between two circular interpolations is replaced by discontinuity in curvature by adding a fillet which is in relation to the functional tolerance ε imposed in the part design. An experimental study has been carried out to validate the models
Quantum interferometry with three-dimensional geometry
Quantum interferometry uses quantum resources to improve phase estimation
with respect to classical methods. Here we propose and theoretically
investigate a new quantum interferometric scheme based on three-dimensional
waveguide devices. These can be implemented by femtosecond laser waveguide
writing, recently adopted for quantum applications. In particular, multiarm
interferometers include "tritter" and "quarter" as basic elements,
corresponding to the generalization of a beam splitter to a 3- and 4-port
splitter, respectively. By injecting Fock states in the input ports of such
interferometers, fringe patterns characterized by nonclassical visibilities are
expected. This enables outperforming the quantum Fisher information obtained
with classical fields in phase estimation. We also discuss the possibility of
achieving the simultaneous estimation of more than one optical phase. This
approach is expected to open new perspectives to quantum enhanced sensing and
metrology performed in integrated photonic.Comment: 7 pages (+4 Supplementary Information), 5 figure
Numerical simulation on onset characteristics of traveling-wave thermoacoustic engines based on a time-domain network model
Onset characteristics of thermoacoustic engines are of great importance for understanding the internal working mechanisms of thermoacoustic conversion. A one-dimensional time-domain network model for predicting the onset characteristics of traveling-wave thermoacoustic engines with helium as working gas is built. The acoustic resistance, inertance, compliance, and thermal-relaxation effects of all the acoustic components are included. The viscous and heat transfer terms in the time-domain governing equations of the acoustic tubes and the heat exchangers are deduced from the frequency-domain linear thermoacoustic theory. Combining the time-domain governing equations of the regenerator, numerical simulations of the whole onset process are then conducted in a wide operating condition range. The complete dynamic pressure wave evolution processes are simulated successfully. It is shown that a steady standing-wave acoustic field forms in almost all parts of the traveling-wave thermoacoustic engine except for the regenerator area. Onset temperature, operating frequency, and quality factor are calculated with a relatively high accuracy. The thermal relaxation effects in the regenerator are found to have a remarkable impact on the onset characteristics, especially at high mean pressures. It is also shown that the experimental damping temperature is closer to the calculated onset temperature than the experimental onset temperature. Furthermore, the reasonable distributions of the pressure and volume flow rate and the phase relationship between them in the whole system are obtained and analyzed
Direct generation of photon triplets using cascaded photon-pair sources
Non-classical states of light, such as entangled photon pairs and number
states, are essential for fundamental tests of quantum mechanics and optical
quantum technologies. The most widespread technique for creating these quantum
resources is the spontaneous parametric down-conversion (SPDC) of laser light
into photon pairs. Conservation of energy and momentum in this process, known
as phase-matching, gives rise to strong correlations which are used to produce
two-photon entanglement in various degrees of freedom. It has been a
longstanding goal of the quantum optics community to realise a source that can
produce analogous correlations in photon triplets, but of the many approaches
considered, none have been technically feasible. In this paper we report the
observation of photon triplets generated by cascaded down-conversion. Here each
triplet originates from a single pump photon, and therefore quantum
correlations will extend over all three photons in a way not achievable with
independently created photon pairs. We expect our photon-triplet source to open
up new avenues of quantum optics and become an important tool in quantum
technologies. Our source will allow experimental interrogation of novel quantum
correlations, the post-selection free generation of tripartite entanglement
without post- selection and the generation of heralded entangled-photon pairs
suitable for linear optical quantum computing. Two of the triplet photons have
a wavelength matched for optimal transmission in optical fibres, ideally suited
for three-party quantum communication. Furthermore, our results open
interesting regimes of non-linear optics, as we observe spontaneous
down-conversion pumped by single photons, an interaction also highly relevant
to optical quantum computing.Comment: 7 pages, 3 figures, 1 table; accepted by Natur
A semiconductor source of triggered entangled photon pairs?
The realisation of a triggered entangled photon source will be of great
importance in quantum information, including for quantum key distribution and
quantum computation. We show here that: 1) the source reported in ``A
semiconductor source of triggered entangled photon pairs''[1. Stevenson et al.,
Nature 439, 179 (2006)]} is not entangled; 2) the entanglement indicators used
in Ref. 1 are inappropriate, relying on assumptions invalidated by their own
data; and 3) even after simulating subtraction of the significant quantity of
background noise, their source has insignificant entanglement.Comment: 5 pages in pre-print format, 1 tabl
Synthesis and structural characterization of a mimetic membrane-anchored prion protein
During pathogenesis of transmissible spongiform encephalopathies (TSEs) an abnormal form (PrPSc) of the host encoded prion protein (PrPC) accumulates in insoluble fibrils and plaques. The two forms of PrP appear to have identical covalent structures, but differ in secondary and tertiary structure. Both PrPC and PrPSc have glycosylphospatidylinositol (GPI) anchors through which the protein is tethered to cell membranes. Membrane attachment has been suggested to play a role in the conversion of PrPC to PrPSc, but the majority of in vitro studies of the function, structure, folding and stability of PrP use recombinant protein lacking the GPI anchor. In order to study the effects of membranes on the structure of PrP, we synthesized a GPI anchor mimetic (GPIm), which we have covalently coupled to a genetically engineered cysteine residue at the C-terminus of recombinant PrP. The lipid anchor places the protein at the same distance from the membrane as does the naturally occurring GPI anchor. We demonstrate that PrP coupled to GPIm (PrP-GPIm) inserts into model lipid membranes and that structural information can be obtained from this membrane-anchored PrP. We show that the structure of PrP-GPIm reconstituted in phosphatidylcholine and raft membranes resembles that of PrP, without a GPI anchor, in solution. The results provide experimental evidence in support of previous suggestions that NMR structures of soluble, anchor-free forms of PrP represent the structure of cellular, membrane-anchored PrP. The availability of a lipid-anchored construct of PrP provides a unique model to investigate the effects of different lipid environments on the structure and conversion mechanisms of PrP
MicroRNA expression, survival, and response to interferon in liver cancer
BACKGROUND: Hepatocellular carcinoma is a common and aggressive cancer that occurs mainly in men. We examined microRNA expression patterns, survival, and response to interferon alfa in both men and women with the disease. METHODS: We analyzed three independent cohorts that included a total of 455 patients with hepatocellular carcinoma who had undergone radical tumor resection between 1999 and 2003. MicroRNA-expression profiling was performed in a cohort of 241 patients with hepatocellular carcinoma to identify tumor-related microRNAs and determine their association with survival in men and women. In addition, to validate our findings, we used quantitative reverse-transcriptase-polymerase- chain-reaction assays to measure microRNAs and assess their association with survival and response to therapy with interferon alfa in 214 patients from two independent, prospective, randomized, controlled trials of adjuvant interferon therapy. RESULTS: In patients with hepatocellular carcinoma, the expression of miR-26a and miR-26b in nontumor liver tissue was higher in women than in men. Tumors had reduced levels of miR-26 expression, as compared with paired noncancerous tissues, which indicated that the level of miR-26 expression was also associated with hepatocellular carcinoma. Moreover, tumors with reduced miR-26 expression had a distinct transcriptomic pattern, and analyses of gene networks revealed that activation of signaling pathways between nuclear factor κB and interleukin-6 might play a role in tumor development. Patients whose tumors had low miR-26 expression had shorter overall survival but a better response to interferon therapy than did patients whose tumors had high expression of the microRNA. CONCLUSIONS: The expression patterns of microRNAs in liver tissue differ between men and women with hepatocellular carcinoma. The miR-26 expression status of such patients is associated with survival and response to adjuvant therapy with interferon alfa. Copyright © 2009 Massachusetts Medical Society. All rights reserved.published_or_final_versio
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