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Results for “Continuous Evolution”

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At least 343 records · Page 19Linked to original sources

PubMed2003

Quantum information in cavity quantum electrodynamics: logical gates, entanglement engineering and 'Schrödinger-cat states'.

In cavity-quantum-electrodynamics experiments, two-level Rydberg atoms and single-photon microwave fields can be seen as qubits. Quantum gates based on resonant and dispersive atom-field effects have been realized, which implement various kinds of conditional dynamics between these qubits. We have also studied the interaction between a single atom and coherent fields stored in the cavity. By progressively increasing the number of photons in these fields, we have explored various aspects of the quantum-classical boundary. We have realized a complementarity experiment demonstrating the continuous evolution of an apparatus from a quantum to a classical behaviour. We have also prepared 'Schrödinger-cat'-like states of the field made of a few photons, and observed their decoherence. We present a brief review of these experiments along with a proposal to study larger systems, i.e. coherent fields with more photons. Fundamental limits to the size of mesoscopic superpositions of field states in a cavity will be briefly discussed.

Journal Article↗

PubMed2003

Information, knowledge and the future of machines.

This wide-ranging survey considers the future of machines in terms of information, complexity and the growth of knowledge shared amongst agents. Mechanical and human agents are compared and contrasted, and it is argued that, for the foreseeable future, their roles will be complementary. The future development of machines is examined in terms of unions of human and machine agency evolving as part of economic activity. Limits to, and threats posed by, the continuing evolution of such a society of agency are considered.

Artificial Intelligence↗

PubMed1999

Effects of quenched disorder on the orientational order of the octylcyanobiphenyl liquid crystal.

Deuteron NMR (DNMR) measurements were performed with high-temperature and spectral resolution on the octylcyanobiphenyl (8CB) liquid crystal confined to the randomly interconnected pores of silica aerogel as a function of temperature and silica density. The aerogel density was varied by one order of magnitude and the temperature spanned the isotropic (I), nematic (N), and smectic-A (SmA) phases of 8CB. For all samples, the liquid crystal was confined to pores smaller than the micron-sized magnetic coherence length. Thus the observed line shapes reflect the director pattern, n(r-->), and the orientational order, Q, as dictated by the porous host. The DNMR spectral patterns are consistent with powder line shapes representative of a randomized n(r-->) characterized by a single Q. The nematic domains formed are of finite dimension that likely exceeds the confining size. The weakly first-order nematic-to-isotropic phase transition becomes less discontinuous with decreasing pore size, eventually becoming continuous at an aerogel density between 0.36 and 0.5 g/cm(3). In the most severe confinement, no phase transitions are observed with only a continuous evolution of Q present. The orientational order is suppressed from the bulk's with no enhancement upon the onset of the SmA phase. This indicates a decoupling of nematic and smectic order parameters and a severe suppression of the SmA phase by this porous media.

Journal Article↗

PubMed2000

Reverse and intermediate segregation of large beads in dry granular media

Mixtures of two types of glass beads have been sheared in a chute flow, in a half-filled rotating drum, and placed in a funnel to form a pile. In the three experimental devices, for small size ratios, there is a segregation of the large beads at the surface of the flowing phase (usual case), but for high size ratios (above about 5) the large beads segregate inside (reverse segregation). Precise measurements show that the segregation drives the large beads to an intermediate level inside the bed. In all devices, there is a continuous evolution of the location of the segregated beads from the surface to deep inside, when increasing the size ratio between the beads. The location of the segregated beads at intermediate levels is well defined both for high size ratios (above 5) and for very small size ratios (about 2), the level being very close to the surface in that case. The reverse and intermediate segregations are masked when using high fractions of large beads in the experiments. Their interpretation involves the high mass of the large particles balancing geometrical effects at a particular intermediate level inside the flowing layer.

Journal Article↗

PubMed2004

Ferroelectric smectic- C* liquid-crystal phase: reexamination of the electric-field influence.

Calorimetric and dielectric experiments are presented near the recently proposed Lifshitz point in order to study the nature and properties of the newly suggested phase transitions in the electric-field-temperature (E-T) phase diagram. It was found that both calorimetric and dielectric results obtained across the recently proposed C1 - C2 transition line agree with the predictions of the extended Landau model, showing that the C1 - C2 transition line is not a true phase transition but is merely a continuous evolution similar to a supercritical evolution between two states possessing microscopically the same symmetry. However, it was confirmed in agreement with findings by Ghoddoussi et al. that in samples of finite thickness the extended Landau model cannot adequately describe some features of the E-T phase diagram and some other physical quantities such as the Goldstone mode temperature dependence and the polarization field dependence P (E) . These discrepancies are discussed within the frame of a relaxing mechanism of the helicoidal structure involving annihilation of pairs of +/-2pi disclination lines.

Journal Article↗

PubMed2006

Transport theory at the nanoscale. II. Interface dynamics for film growth.

Conditions for surface nucleation and growth of a film are determined in a diffuse interface model. A method is given, derived from a Fokker-Planck equation for the nonequilibrium particle distribution, which links atomic and mesoscopic events in a rheological description similar to the classical continuum theory of fluid flow. Film nucleation and growth are modeled by the spatially inhomogeneous continuous evolution of the instantaneous density profile which measures the average number of particles or molecules at given time and position. It is shown how an alteration in the distribution of particles in the vicinity of the boundary between parent and product phases induces transient film growth and damped vibrations at the surface. The method is general but as an illustration, the condensation of a simple classical fluid on cooling is considered in detail.

Journal Article↗

PubMed2006

Investigations of nanoscale helical pitch in smectic-Calpha and smectic-C phases of a chiral smectic liquid crystal using differential optical reflectivity measurements.

Differential optical reflectivity (DOR) was used to study the temperature dependence of the short helical pitch in freestanding films of a liquid crystal compound. The experimentally measured DOR signal was fitted using Berreman's 4 x 4 matrix method to get the pitch value in the smectic-C*alpha (sMC*alpha) phase. The results show continuous evolution of the pitch between the smectic-C*alpha and sMC*alpha phases. In sMC*alpha, the pitch decreases as temperature increases and is found to level off at 16+/-1 smectic layers at the sMC*alpha to smectic-A* transition.

Journal Article↗

PubMed2000

Coulomb gap: how a metal film becomes an insulator

Electron tunneling measurements of the density of states (DOS) in ultrathin Be films reveal that a correlation gap mediates their insulating behavior. In films with sheet resistance R<5000 Omega the correlation singularity appears as the usual perturbative ln(V) zero bias anomaly (ZBA) in the DOS. As R is increased further, however, the ZBA grows and begins to dominate the DOS spectrum. This evolution continues until a nonperturbative |V| Efros-Shklovskii Coulomb gap spectrum finally emerges in the highest R films. Transport measurements of films which display this gap are well described by a universal variable range hopping law R(T) = (h/2e(2))exp(T0/T)(1/2).

Journal Article↗

PubMed2002

Liquid-liquid phase transition in elemental carbon: a first-principles investigation.

It has been recently suggested that elemental carbon may be a promising candidate to exhibit a liquid-liquid phase transition (LLPT). We report the results of first-principles molecular dynamics simulations showing no evidence of LLPT in carbon, in the same temperature and pressure range where such a transition was found using empirical calculations. Our simulations indicate a continuous evolution from a primarily sp-bonded liquid to an sp(2)-like and an sp(3)-like fluid, as a function of pressure, above the graphite melting line. The discrepancy between quantum and classical simulations is attributed to the inability of empirical potentials to describe complex electronic effects in condensed carbon phases.

Journal Article↗

PubMed2004

Magnetic properties of (BEDT-TTF)(ClMeTCNQ) studied by ESR under pressure: a neutral-ionic crossover and thermoinduced mesophase.

The neutral-ionic (NI) phase transition in (BEDT-TTF)(ClMeTCNQ) is studied with ESR under pressure to tune the transition temperature. Broad peak structures observed in the spin susceptibility around T(NI) are analyzed with the assumption of a spin-Peierls gap of 1100 K, which demonstrates the continuous evolution of ionic domain fraction through T(NI) over the extent T(W) proportional, variantT(NI). An unexpected feature is the presence of sizable ionic droplets even at T>>T(NI), which is ascribed to the tiny energy difference between the two phases.

Journal Article↗

PubMed2005

Efficient quantum monte carlo energies for molecular dynamics simulations.

A method is presented to treat electrons within the many-body quantum Monte Carlo (QMC) approach "on-the-fly" throughout a molecular dynamics (MD) simulation. Our approach leverages the large (10-100) ratio of the QMC electron to MD ion motion to couple the stochastic, imaginary-time electronic and real-time ionic trajectories. This continuous evolution of the QMC electrons results in highly accurate total energies for the full dynamical trajectory at a fraction of the cost of conventional, discrete sampling. We show that this can be achieved efficiently for both ground and excited states with only a modest overhead to an ab initio MD method. The accuracy of this dynamical QMC approach is demonstrated for a variety of systems, phases, and properties, including optical gaps of hot silicon quantum dots, dissociation energy of a single water molecule, and heat of vaporization of liquid water.

Journal Article↗

PubMed1974

The effect of light on the tricarboxylic Acid cycle in green leaves: I. Relative rates of the cycle in the dark and the light.

Excised green leaves of mung bean (Phaseolus aureus L. var. Mungo) were used to determine the effect of light on the rate of endogenous respiration via the tricarboxylic acid cycle. Illumination with white light at an intensity of 0.043 gram calories cm(-2)min(-1) (approximately 8600 lux) of visible radiation (400-700 nm) gave a rate of apparent photosynthesis, measured as net CO(2) uptake, of 21 mg CO(2) dm(-2)hr(-1) which was about 11-fold greater than the rate of dark respiration. The feeding of (14)CO(2) or (14)C-labeled acids of the tricarboxylic acid cycle in the dark for 2 hours was established as a suitable method for labeling mitochondrial pools of cycle intermediates.At a concentration of 0.1 mm 3-(3,4-dichlorophenyl)-1,1-dimethylurea, apparent photosynthesis was inhibited 82%, and the refixation of (14)CO(2) derived internally from endogenous respiration was largely prevented. In the presence of this inhibitor endogenous respiration, measured as (14)CO(2) evolution, continued in the light at a rate comparable to that in the dark. Consequently, under these conditions light-induced nonphotosynthetic processes have no significant effect on endogenous dark respiration. Inhibitors of the tricarboxylic acid cycle, malonate and fluoroacetate, were used to determine the relative rates of carbon flux through the cycle in the dark and in the light by measuring the rate of accumulation of (14)C in either succinate or citrate. Results were interpreted to indicate that the tricarboxylic acid cycle functions in the light at a rate similar to that in the dark except for a brief initial inhibition on transition from dark to light. Evidence was obtained that succinate dehydrogenase as well as aconitase, was inhibited in the presence of fluoroacetate.

Journal Article↗

PubMed1981

Wound-induced Ethylene Formation in Albedo Tissue of Citrus Fruit.

Excised albedo tissue of citrus fruit (Citrus unshiu and Citrus hassaku) produced ethylene at an increasing rate in response to wounding and aging. The application of 1-aminocyclopropane-1-carboxylic acid (ACC) enhanced ethylene production in both the fresh and aged tissues, but this increase was greater in the aged tissue than in the fresh tissue. ACC content was very low in fresh tissue but increased greatly in aging tissue, paralleling the rise in ethylene production. Aminoethoxyvinylglycine (AVG) strongly inhibited ethylene production in the aged tissue. In the presence of ACC, however, ethylene production was not inhibited by AVG. These results suggest that ACC is an intermediate in the pathway of ethylene biosynthesis in the albedo tissue and that both steps of ACC formation and ACC conversion to ethylene are enhanced by wounding and aging. Inhibitors of protein synthesis, cycloheximide and 2-(4-methyl-2,6-dinitroanilino)-N-methyl propionamide, strongly inhibited ethylene production in the albedo tissue, implying that protein synthesis is required to maintain the continuous evolution of ethylene. The stimulation of ethylene production by ACC was reduced by the addition of l-methionine, whereas d-methionine had very little inhibitory effect. Ethylene production in the albedo tissue was also inhibited by the addition of n-propyl gallate and 3,5-dibromo-4-hydroxybenzoic acid.

Journal Article↗

PubMed1996

Adhesive and migratory behaviors of nevus cells differ from those of epidermal melanocytes and are not linked to the histological type of nevus.

It has been postulated that acquired nevi undergo life span continuous evolution from junctional, presumably in radial expanding phase at the dermal epidermal junction, to compound and then to dermal nested nevi. In an attempt to correlate the morphology of nevi with biological data, we have investigated whether migratory and adhesive phenotypes of nevus cells could account for histological patterns and possible spatiotemporal changes in nevi. Nevus cells were cultured from compound and dermal nevi and compared to normal epidermal cultured melanocytes from children and adults. AR nevus cells showed similar in vitro adhesive and migratory indexes on laminin-1, laminin-5/nicein, fibronectin, or collagen IV substrates, suggesting that these intrinsic characteristics do not account for the tendency to dermal nesting and/or to radial growth along the dermal-epidermal junction. The cells from epidermal and dermal parts of compound nevi migrated similarly across a reconstituted basement membrane. The results show that intrinsic adhesive and migratory behaviors of nevus cells were not associated with a histological type of nevus. Interestingly, differences in migratory phenotype and intercellular adhesion capacities between nevus cells and normal melanocytes indicated that they could represent different melanocytic cell subpopulations. Finally, melanocytes from adults and children expressed similar levels of the same integrins as all nevus cells but showed differences in function of both alpha3 and alpha6 integrin subunits and in migratory/adhesive behaviors, which may suggest different states of melanocyte maturation.

Adult↗

PubMed1989

The therapeutic community: exploring the boundaries.

The past 20 years have demonstrated the effectiveness of therapeutic community (TC) treatment for drug abuse as it evolved in the United States. We now better understand the influence that psychodynamic features of TC treatment have on character disorder. Best perceived as a setting designed--as society is not--to encourage and support social learning, the TC has succeeded in modifying its programs and adapting self-help methods to serve drug abusers of all kinds and abusers of all drugs. Continued evolution of the TC depends upon development of its already-demonstrated capacity to affect disordered behaviour other than drug abuse. The growth of disordered populations in the United States and increasingly in Great Britain gives urgency to such future employment. Therapeutic communities and TC-like programs for non-drug abusers already exist. But widespread use depends upon strengthening the theoretical underpinnings of TC treatment and establishing closer working relationships between TC's and mainstream medical, mental health and social service institutions.

Humans↗

PubMed2004

Outbreak of West Nile virus causing severe neurological involvement in children, Nuba Mountains, Sudan, 2002.

An atypical outbreak of West Nile virus (WNV) occurred in Ngorban County, South Kordophan, Sudan, from May to August 2002. We investigated the epidemic and conducted a case-control study in the village of Limon. Blood samples were obtained for cases and controls. Patients with obvious sequelae underwent cerebrospinal fluid (CSF) sampling as well. We used enzyme-linked immunosorbent assay (ELISA) and neutralization tests for laboratory diagnosis and identified 31 cases with encephalitis, four of whom died. Median age was 36 months. Bivariate analysis did not reveal any significant association with the risk factors investigated. Laboratory analysis confirmed presence of IgM antibodies caused by WNV in eight of 13 cases, indicative of recent viral infection. The unique aspects of the WNW outbreak in Sudan, i.e. disease occurrence solely among children and the clinical domination of encephalitis, involving severe neurological sequelae, demonstrate the continuing evolution of WNV virulence. The spread of such a virus to other countries or continents cannot be excluded.

Case-Control Studies↗

PubMed1999

Contraceptive use in Australia: evidence from the 1995 National Health Survey.

This paper analyses the patterns of contraceptive use among Australian women, using data from the 1995 National Health Survey. More than 44% of all women aged 18-49 years reported using a method of contraception. Among users, the 2 most commonly reported methods were the pill (60%) and condom (27%); IUD and natural methods accounted for less than 5% each. Sterilizing operations of the women/partner were the most frequently reported reasons for nonuse of contraception in women aged over 35 years, while among the younger women the most reported reasons were pregnancy or trying to get pregnant and not being sexually active. Among pill-users about a quarter were smokers, 20% overweight and 13% reported heart or circulatory disease. These figures were generally lower than in the general population but indicate a need for regular monitoring. The survey demonstrates the continuing evolution in the use of contraception among Australian women.

Adolescent↗

PubMed1993

Delayed success following radiofrequency catheter ablation.

Two patients who underwent attempted radiofrequency catheter ablation of an atrioventricular accessory pathway experienced delayed abolition of pathway conduction. During the procedures there was transient block in the accessory pathway following multiple ablation attempts at closely spaced sites. Both patients showed evidence of preexcitation at the conclusion of the ablation session but neither showed evidence of accessory pathway conduction during a second electrophysiological study. These observations demonstrate that in patients in whom transient block of the accessory pathway is produced, continued evolution of radiofrequency energy lesions may result in the eventual success of an initially unsuccessful ablation session.

Adenosine↗