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At least 703 records · Page 39Linked to original sources

PubMed2004

Observation of spinor dynamics in optically trapped 87Rb Bose-Einstein condensates.

We measure spin mixing of F=1 and F=2 spinor condensates of 87Rb atoms confined in an optical trap. We determine the spin mixing time to be typically less than 600 ms and observe spin population oscillations. The equilibrium spin configuration in the F=1 manifold is measured for different magnetic fields and found to show ferromagnetic behavior for low field gradients. An F=2 condensate is created by microwave excitation from the F=1 manifold, and this spin-2 condensate is observed to decay exponentially with time constant 250 ms. Despite the short lifetime in the F=2 manifold, spin mixing of the condensate is observed within 50 ms.

Journal Article↗

PubMed2005

Formation dynamics of a fermion pair condensate.

The dynamics of pair condensate formation in a strongly interacting Fermi gas close to a Feshbach resonance was studied. We employed a phase-shift method in which the delayed response of the many-body system to a modulation of the interaction strength was recorded. The observable was the fraction of condensed molecules in the cloud after a rapid magnetic field ramp across the Feshbach resonance. The measured response time was slow compared to the rapid ramp, which provides final proof that the molecular condensates reflect the presence of fermion pair condensates before the ramp.

Journal Article↗

PubMed2005

Complex chemical potential: signature of decay in a bose-einstein condensate.

We explore the zero-temperature statics of an atomic Bose-Einstein condensate in which a Feshbach resonance creates a coupling to a second condensate component of quasibound molecules. Using a variational procedure to find the equation of state, the appearance of this binding is manifest in a collapsing ground state, where only the molecular condensate is present up to some critical density. Further, an excited state is seen to reproduce the usual low-density atomic condensate behavior in this system, but the molecular component is found to produce a coherent, many-body decay, quantified by the imaginary part of the chemical potential. Most importantly, the unique decay rate dependencies on density (approximately rho (3/2)) and on scattering length (approximately (5/2)) can be measured in experimental tests of this result.

Journal Article↗

PubMed2005

Anomalous quantum reflection of Bose-Einstein condensates from a silicon surface: the role of dynamical excitations.

We investigate the effect of interatomic interactions on the quantum-mechanical reflection of Bose-Einstein condensates from regions of rapid potential variation. The reflection process depends critically on the density and incident velocity of the condensate. For low densities and high velocities, the atom cloud has almost the same form before and after reflection. Conversely, at high densities and low velocities, the reflection process generates solitons and vortex rings that fragment the condensate. We show that this fragmentation can explain the anomalously low reflection probabilities recently measured for low-velocity condensates incident on a silicon surface.

Journal Article↗

PubMed2005

Dynamical instability and domain formation in a spin-1 Bose-Einstein condensate.

We interpret the recently observed spatial domain formation in spin-1 atomic condensates as a result of dynamical instability. Within the mean field theory, a homogeneous condensate is dynamically unstable (stable) for ferromagnetic (antiferromagnetic) atomic interactions. We find that this dynamical instability naturally leads to spontaneous domain formation as observed in several recent experiments for condensates with rather small numbers of atoms. For trapped condensates, our numerical simulations compare quantitatively to the experimental results, thus largely confirming the physical insight from our analysis of the homogeneous case.

Journal Article↗

PubMed2005

Condensation of classical nonlinear waves.

We study the formation of a large-scale coherent structure (a condensate) in classical wave equations by considering the defocusing nonlinear Schrödinger equation as a representative model. We formulate a thermodynamic description of the classical condensation process by using a wave turbulence theory with ultraviolet cutoff. In three dimensions the equilibrium state undergoes a phase transition for sufficiently low energy density, while no transition occurs in two dimensions, in complete analogy with standard Bose-Einstein condensation in quantum systems. On the basis of a modified wave turbulence theory, we show that the nonlinear interaction makes the transition to condensation subcritical. The theory is in quantitative agreement with the numerical integration of the nonlinear Schrödinger equation.

Journal Article↗

PubMed2006

Condensation transition in DNA-polyaminoamide dendrimer fibers studied using optical tweezers.

When mixed together, DNA and polyaminoamide dendrimers form fibers that condense into a compact structure. We use optical tweezers to pull condensed fibers and investigate the decondensation transition by measuring force-extension curves (FECs). A characteristic force plateau (around 10 pN) and hysteresis between the pulling and relaxation cycles are observed for different dendrimer sizes, indicating the existence of a first-order transition between two phases (condensed and extended) of the fiber. Upon salt variation FECs change noticeably confirming that electrostatic forces drive the condensation transition. We propose a simple model for the decondensing transition that qualitatively reproduces the FECs and which is confirmed by atomic force microscopy images.

Bacteriophage lambda↗

PubMed2006

Spin-3 chromium Bose-Einstein condensates.

We analyze the physics of spin-3 Bose-Einstein condensates, and, in particular, the new physics expected in ongoing experiments with condensates of chromium atoms. We first discuss the ground-state properties, which, depending on still unknown chromium parameters, and for low magnetic fields, can present various types of phases. We also discuss the spinor dynamics in chromium spinor condensates, which present significant qualitative differences when compared to other spinor condensates. In particular, dipole-induced spin relaxation may lead for low magnetic fields to transfer of spin into angular momentum similar to the well-known Einstein-de Haas effect. Additionally, a rapid large transference of population between distant magnetic states also becomes possible.

Journal Article↗

PubMed2001

Verification of NEXAFS assignments by a comparison of fragmentation between gaseous and condensed methyl formate.

According to the ion desorption from condensed methyl formate (DCOOCH3) by C 1s electron excitation, C+ yield was strongly enhanced at 289.1 eV, a higher energy side of C1s(DC) --> pi*(C=O) peak. This feature could not be clearly assigned. In this work, to clarify the feature, fragment-ion yield curves of gas-phase methyl formate were measured and compared with those of condensed one, since gas-phase and condensed systems are presumed to show more or less similar fragment-ion yield curves under similar excitations. The results demonstrate that fragment-ion yield curves are useful for the assignments of NEXAFS features in both gaseous and condensed polyatomic molecules.

Journal Article↗

PubMed1985

Moisture-conserving efficiency of condenser humidifiers.

The moisture-conserving efficiency of commercially available condenser humidifiers (small, disposable, airway humidifiers) was studied. A comprehensive comparison of all currently available condenser humidifiers utilising a laboratory system which simulated a breathing, intubated patient in temperature, humidity, dead space, and respiratory pattern characteristics was undertaken. The percentage of moisture conserved, or efficiency, of the humidifiers was calculated gravimetrically from the water loss of the testing system with and without the condenser humidifiers. The Portex Humid-Vent and Trach-Vent, Siemens Servo 150 and the Terumo Brethaia were evaluated. The data revealed an inverse correlation between efficiency and tidal volume. The most efficient were the Portex Humid-Vent at low tidal volumes and Siemens Servo 150 at the mid and high tidal volumes. To achieve a minimum inspired water content of 33 mg H2O/litre gas, a 79% condenser humidifier efficiency is necessary. None of these units met this requirement; however, they may be appropriate for limited clinical application.

Anesthesia, Inhalation↗

PubMed1993

An in vitro study of the quality of root fillings in teeth obturated by lateral condensation of gutta-percha or Thermafil obturators.

The aim of this in vitro study was to assess the quality of root canal obturation and degree of linear apical dye penetration in teeth root filled with either laterally condensed gutta-percha or Thermafil obturators. A total of 150 teeth with single roots were included in the study. All canals were prepared using a standard step-back technique with anticurvature filing. Radiographs taken of the teeth to show the maximum degree of canal curvature were then exposed and the angle, radius and position of curvature determined. This information about the canals, together with their working length and diameter at end-point, was used to divide the teeth into two experimental and two control groups. A total of eight teeth were excluded because of technical difficulties, 65 were filled with Thermafil obturators, 63 were filled with laterally condensed gutta-percha whilst 14 teeth remained unfilled and acted as controls. Following obturation, the teeth were radiographed in two planes and the technical quality of fill assessed on a four-point scale. All access cavities were then sealed and the teeth immersed in dye for 48 h before being split longitudinally. Linear dye penetration via the apical foramen was then assessed. Canal obturation with Thermafil obturators (0.7 min) was significantly quicker (P < 0.001) than lateral condensation (6.4 min). Apical extrusion of sealer and gutta-percha occurred significantly more often with Thermafil obturators but there was little difference in the technical quality of the fillings and no significant difference in dye penetration. Under the conditions of this study. Thermafil obturators proved a satisfactory alternative to lateral condensation of gutta-percha.

Chi-Square Distribution↗

PubMed1994

A laboratory study of root fillings in teeth obturated by lateral condensation of gutta-percha or Thermafil obturators.

The aim of this in vitro study was to assess the quality of root canal obturation and degree of apical dye penetration in teeth root-filled with either laterally condensed cold gutta-percha or Thermafil obturators. A total of 144 extracted teeth with single roots were included in the study. All canals were prepared with a standard technique using a sonic handpiece with copious irrigation. Radiographs taken of the teeth to show the maximum degree of canal curvature were then exposed and the angle, radius and position of curvature determined. This information about the canals, together with their working length and diameter at end-point was used to divide the teeth into two experimental and two control groups. A total of 71 teeth were filled with Thermafil obturators, 69 with lateral condensation while four teeth remained unfilled and acted as controls. Following obturation, the teeth were radiographed in two planes and the technical quality of fill assessed on a four-point scale. All access cavities were then sealed and the teeth immersed in dye for 48 h before being split longitudinally. Linear dye penetration via the apical foramen was then assessed. In both straight and curved canals obturation with Thermafil obturators was significantly quicker (P < 0.001) then lateral condensation. Apical extrusion of gutta-percha occurred significantly more often in straight canals obturated with lateral condensation (P < 0.005) but there was no difference in curved canals. There was little difference in the radiographic quality of fill in the apical halves of the root fillings but Thermafil obturators were significantly better in the coronal halves when viewed from the proximal.(ABSTRACT TRUNCATED AT 250 WORDS)

Chi-Square Distribution↗

PubMed2004

Root canal obturation by ultrasonic condensation of gutta-percha. Part II: an in vitro investigation of the quality of obturation.

AIM: To compare the quality of root canal obturation using ultrasonic or cold condensation of gutta-percha and to determine the effect of power setting and activation time on the quality of obturation using the former technique. METHODOLOGY: An extracted human maxillary canine was used in an in vitro split tooth model to allow repeated obturation of the same root canal system using an ultrasonic device to thermocompact gutta-percha without sealer. After each obturation, the root filling was removed from the tooth to allow evaluation of its quality and for the tooth to be re-obturated. The influence of combinations (n = 10 per combination) of power setting (1, 3, 5) and activation times (4, 10, 15 s) was tested on the quality of root filling, assessed by measuring the voids within the body of the root filling as well as at the surface. Image analysis was used to quantify the voids within the body of the root filling. Cold lateral condensation of gutta-percha served as a control. RESULTS: Both surface and cross-sectional analyses revealed that different power setting and activation time combinations produced significantly fewer voids than cold lateral condensation (P < 0.05) at the apical, mid-root and coronal levels. CONCLUSIONS: Taking surface and cross-sectional analysis together only power setting 5 and activation times of 10 and 15 s consistently produced ultrasonically thermocompacted root canal fillings with fewer voids than cold lateral condensation without sealer.

Cold Temperature↗

PubMed1985

Automated thermatic condensation of gutta-percha root fillings in teeth with open (immature) apices.

Forty upper human premolar teeth with open (immature) apices were root filled by one of three methods, namely lateral condensation with sealer, automated thermatic condensation with sealer, and automated thermatic condensation without sealer. The completed root fillings were then assessed for apical defects, apical extrusions, radiographic voids, apical seal and surface adaptation. The majority of the results indicate that the automated thermatic technique without sealer produces marginally better root fillings in teeth with open apices than the other two methods. However, it is impossible to say whether this would confer any clinical advantage on the technique. The authors recommend that clinicians who wish to use the automated thermatic technique for condensing gutta-percha become highly proficient before its use on patients.

Bicuspid↗

PubMed1992

Sequential induction of syndecan, tenascin and cell proliferation associated with mesenchymal cell condensation during early tooth development.

The cell surface proteoglycan, syndecan, and the extracellular matrix glycoprotein, tenascin, are expressed in the mesenchyme during early development of many organs. We have studied the expression patterns of syndecan and tenascin during initiation of tooth development and in association with mesenchymal cell condensation and compared these with cell proliferation. Syndecan, tenascin and bromodeoxyuridine (BrdU) incorporation were localized by triple-labelling immunohistochemistry in serial sections of molar tooth germs of mouse embryos. Prior to formation of the epithelial tooth bud, syndecan accumulated in the mesenchymal cells which underlie the presumptive dental epithelium, but tenascin was not detected at this stage. Tenascin appeared during initiation of the epithelial down-growth at the lingual aspect of the tooth germ. During subsequent formation of the epithelial bud, at the late bud stage, syndecan and tenascin became exactly colocalized in the condensed mesenchyme which was clearly demarcated from other jaw mesenchyme. The expression of syndecan and tenascin was accompanied by rapid cell proliferation as indicated by marked BrdU incorporation. When development advanced to the cap stage, syndecan staining intensity in the dental papilla mesenchyme increased further whereas tenascin became reduced. In conclusion, the results demonstrate that the expression patterns of syndecan and tenascin overlap transiently during the period of mesenchymal cell condensation and that this is accompanied by cell proliferation. Syndecan and tenascin may play a role in growth control and in compartmentalization of the dental mesenchymal cells in the condensate.

Animals↗

PubMed1999

Modulation of drug-metabolising enzyme expression by condensation products of indole-3-ylcarbinol, an inducer in cruciferous vegetables.

Indole-3-ylcarbinol (13C) is formed during processing of cruciferous vegetables and is suggested to be one of the modulators of drug-metabolising enzymes. Indole-3-ylcarbinol is a far less efficient inducer of hepatic enzymes after parenteral than after oral administration, due to formation of active metabolites in the gastrointestinal tract. As indole-3-ylcarbinol is unstable in weakly acidic aqueous solutions, non-active condensation products may be formed from indole-3-ylcarbinol, that cannot be transformed to the active products when reaching the stomach. The purpose of the present study was to test the ability of the condensation products formed at a pH corresponding to that of fresh vegetable juice to modulate the metabolism of xenobiotics. Indole-3-ylcarbinol was incubated in vitro at room temperature in the dark at pH 5.5 and samples taken at various times, for oral administration to rats and for chemical analysis. Indole-3-ylcarbinol was rapidly transformed into various oligomeric products. The 7-ethoxyresorufin O-deethylase activities (marker of cytochrome Cytochrome P450 1A enzymes, CYP1A) in liver, kidney and colon increased with the duration of the in vitro condensation period whereas the formation of 6beta-, 15beta- and and 2alpha-hydroxytestosterone was not affected significantly, indicating no effect on CYP2C11 or CYP3A enzymes. The hepatic metabolism of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). was increased by indole-3-ylcarbinol condensation products and the 4'-OH-PhIP/N-OH-PhIP ratio was decreased due to a significantly increased formation of the proximate genotoxic metabolite. N-OH-PhIP. The activities of DT-diaphorase and glutathione S-transferase were not changed significantly in the rat organs. These experiments clearly indicate that indole-3-ylcarbinol is not the definitive CYP1A inducer and that indole-3-ylcarbinol at near-neutral pH, is transformed to compounds that are inducers by themselves or may be further converted into inducing compounds in the rat stomach. Also, the enzyme inducing potency of indole-3-ylcarbinol containing vegetable juice is apparently enhanced by incubation in vitro before the intake.

Animals↗

PubMed1998

An in vitro comparison of thermoplasticised gutta-percha obturation techniques with cold lateral condensation.

This study compared the apical sealing ability, obturation time and extrusion of gutta-percha and sealer when root canals were obturated using either cold lateral condensation or one of the three methods using thermoplasticised gutta-percha (Alpha Seal, Thermafil or JS Quick Fill) in vitro. One hundred and thirty-one root canals from 78 extracted human teeth were used; 116 canals were divided into five groups so that they were balanced with respect to prepared canal anatomy, and the remaining 15 canals were used as positive and negative controls. The canals in the first four groups were prepared with hand files using the step-down technique to a standard apical size and flare. The last group was prepared using engine-driven rotary nickel-titanium files (McSpadden) to a similar apical size and flare. One of the four obturating techniques was used to fill the canals in each of the first four groups. The fifth group was obturated using the Alpha Seal technique. The roots were immersed in india ink, demineralised and rendered transparent to assess the extent of maximum lincar dye penetration. The Alpha Seal groups had the highest number of specimens without any leakage. There was a significant difference in the proportions of specimens that did not leak when the Alpha Seal (P < 0.01) and cold lateral condensation groups (P < 0.05) were compared with JS Quick Fill. Cold lateral condensation had a higher proportion of specimens with leakage in canals with curvature greater than 20 degrees than in canals with curvatures less than 20 degrees (P < 0.05). The curvature of canals had no effect on the sealing ability of the other techniques. The method of canal preparation had no effect on the sealing ability of Alpha Seal. Alpha Seal, Thermafil and JS Quick Fill were significantly quicker to perform than cold lateral condensation.

Analysis of Variance↗

PubMed1989

An in vitro comparison of the single cone and lateral condensation techniques using 'friction-fitted' and 'solvent dip-fitted' primary gutta-percha cones.

Extracted teeth, root-filled by single cone and lateral condensation techniques, using friction fitted and solvent (chloroform and eucalyptol) dip-fitted primary gutta-percha cones, were compared with respect to apical sealing as measured by length of dye penetration and frequency of no dye penetration. Overall, the single cone techniques were significantly more effective than lateral condensation techniques regarding length of dye penetration. The single cone techniques were not significantly different from the lateral condensation technique which employed chloroform dip-fitted primary gutta-percha cones regarding length of dye penetration. The single cone and lateral condensation techniques which utilized chloroform dip-fitted cones ranked first and second with respect to frequency of no dye penetration.

Chloroform↗