Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Thermal Diffusion”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62Linked to original sources
PubMed2005

Ultrasonic liposuction in the treatment of gynecomastia.

BACKGROUND: Ultrasound-assisted liposuction is a technique that is widely used all over the body for minimal access lipectomy. Recently, it has been reported to be especially suitable for the treatment of gynecomastia. To date, however, there is only one published study that specifically addresses ultrasound-assisted liposuction as a treatment modality for gynecomastia. METHODS: A review was undertaken of all the gynecomastia patients treated with ultrasound-assisted liposuction by a single surgeon over a 3-year period. Thirteen consecutive patients (aged 16 to 57 years) with bilateral, diffuse, soft to moderately firm gynecomastia were studied. RESULTS: There were no early postoperative complications of hematoma, seroma, infection, or thermal injury. Similarly, there were no treatment-induced asymmetries, contour deformities, or irregularities. One patient requested "touch-up" ultrasound-assisted liposuction for "residual" breast tissue several months after an initial satisfactory correction of chest contour. None of the patients required initial open-excision or skin-reduction procedures. Patients were asked to rate their cosmetic results in four categories on linear analogue scales with a maximal score of 10. The average scores were 9.1 for overall satisfaction, 9.2 for scars, 9.2 for shape, and 8.9 for improved self confidence. CONCLUSION: Ultrasound-assisted liposuction is an effective treatment modality in patients with homogenous soft to moderately firm gynecomastia, giving good cosmetic results and a high level of patient satisfaction.

Adolescent↗
PubMed2005

Activated dynamics of semiflexible polymers on structured substrates.

We study the thermally activated motion of semiflexible polymers in double-well potentials using field-theoretic methods. Shape, energy, and effective diffusion constant of kink excitations are calculated, and their dependence on the bending rigidity of the semiflexible polymer is determined. For symmetric potentials, the kink motion is purely diffusive whereas kink motion becomes directed in the presence of a driving force. We determine the average velocity of the semiflexible polymer based on the kink dynamics. The Kramers escape over the potential barriers proceeds by nucleation and diffusive motion of kink-antikink pairs, the relaxation to the straight configuration by annihilation of kink-antikink pairs. We consider both uniform and point-like driving forces. For the case of point-like forces the polymer crosses the potential barrier only if the force exceeds a critical value. Our results apply to the activated motion of biopolymers such as DNA and actin filaments or of synthetic polyelectrolytes on structured substrates.

Biopolymers↗
PubMed2006

The effect of microwave thermal denaturation on release properties of bovine serum albumin and gluten matrices.

The purpose of this study was to compare the effects of denaturation by microwave irradiation on release properties of 2 physically different proteins. Matrices were prepared from water-soluble bovine serum albumin loaded with metoclopramide and sorbed with adequate amount of moisture were thermally denatured in a microwave oven. The release profile of the rather insoluble denatured albumin matrices followed the classical Fickian diffusion profile. The release rate was dependent on the degree of denaturation, which was highly dependent on the level of moisture originally absorbed by the albuminoidal matrices and the period of exposure to microwave energy. Conversely, attempts to reduce the rate of drug release through microwave irradiation of metoclopramide-loaded matrices prepared from water-insoluble gluten were futile. The denaturation process was shown to be limited to the relatively water-soluble protein core fraction, while aggregation between neighboring gluten proteins in the matrix was not achieved even in the presence of considerable amounts of sorbed water.

Diffusion↗
PubMed2004

A new view of occult and obscure gastrointestinal bleeding.

Occult gastrointestinal bleeding usually is discovered when fecal occult blood test results are positive or iron deficiency anemia is detected. Fecal occult blood testing methods vary, but all have limited sensitivity and specificity. The initial work-up for occult bleeding typically involves colonoscopy or esophagogastroduodenoscopy, or both. In patients without symptoms indicating an upper gastrointestinal tract source or in patients older than 50 years, colonoscopy usually is performed first. About one half of patients with gastrointestinal bleeding do not have an obvious source of the bleeding. In those patients, small bowel imaging or repeat panendoscopy may be performed. Barium studies of the small bowel are widely available but have limited diagnostic utility. Mucosal lesions such as vascular ectasias, a common cause of obscure bleeding, may be missed by small bowel studies. Small bowel endoscopy is difficult to perform but has a higher diagnostic yield. Capsule endoscopy is a newer technique that allows noninvasive small bowel imaging. Radionuclide red blood cell scans or angiography may be useful in patients with active bleeding. Treatment of bleeding most often involves endoscopic ablation of the bleeding site with thermal energy, if the site is accessible. Angiographic embolization may be used to treat lesions that cannot be reached endoscopically. Diffuse vascular lesions, which are not uncommon, are difficult to treat. Medical treatment, usually with combined hormone therapy, has limited utility. Surgical treatment of obscure bleeding often fails or is not feasible because of multiple bleeding sites.

Endoscopy, Gastrointestinal↗
PubMed1981

Temperature-dependent inhibition of murine granulocyte-monocyte precursors.

The response of nucleated bone marrow cells from C3H mice to hyperthermic temperatures of 41.5 to 49.5 degrees for a fixed heating period of 30 min has been determined. The threshold temperatures for cell lysis, loss of trypan blue exclusion, and histological evidence of cell injury were greater than 49.5 degrees, 45.5 degrees and 43.5 degrees, respectively. Growth of mature granulocyte-monocytes from precursors was evaluated in Millipore diffusion chamber culture. There was a biphasic decrease in granulocyte-monocyte growth after exposure to temperatures of 41.5 to 45.5 degrees. The ratio of granulocytes to monocytes in proliferated cultures was not altered after hyperthermia. Pluripotent and committed granuloid stem cells were assayed by the spleen colony and plasma clot diffusion chamber techniques. These also showed a biphasic decrease with increase in temperature, with committed stem cells having a greater thermal sensitivity at lower temperatures.

Animals↗
PubMed2003

Fluorescence correlation spectroscopy close to a fluctuating membrane.

Compartmentalization of the cytoplasm by membranes should have a strong influence on the diffusion of macromolecules inside a cell, and we have studied how this could be reflected in fluorescence correlation spectroscopy (FCS) experiments. We derived the autocorrelation function measured by FCS for fluorescent particles diffusing close to a soft membrane, and show it to be the sum of two contributions: short timescale correlations come from the diffusion of the particles (differing from free diffusion because of the presence of an obstacle), whereas long timescale correlations arise from fluctuations of the membrane itself (which create intensity fluctuations by modulating the number of detected particles). In the case of thermal fluctuations this second type of correlation depends on the elasticity of the membrane. To illustrate this calculation, we report the results of FCS experiments carried out close to a vesicle membrane. The measured autocorrelation functions display very distinctly the two expected contributions, and allow both to recover the diffusion coefficient of the fluorophore and to characterize the membrane fluctuations in term of a bending rigidity. Our results show that FCS measurements inside cells can lead to erroneous values of the diffusion coefficient if the influence of membranes is not recognized.

Algorithms↗
PubMed2000

Development of stereotactically guided laser interstitial thermotherapy of breast cancer: in situ measurement and analysis of the temperature field in ex vivo and in vivo adipose tissue.

BACKGROUND AND OBJECTIVE: The size (0.5-1.0 cm) of early nonpalpable breast tumors currently detected by mammography and confirmed by stereotactic core biopsy is of the order of the penetration depth of near infrared photons in breast tissue. In principle, stereotactically biopsied tumors, therefore, could be safely and efficiently treated with laser thermotherapy. The aim of the current study is to confirm the controlled heating produced by clinically relevant power levels delivered with an interstitial laser fiber optic probe adapted for use with stereotactic mammography and biopsy procedures. STUDY DESIGN/MATERIALS AND METHODS: Temperature increases and the resultant thermal field produced by the irradiation of ex vivo (porcine and human) and in vivo (porcine) tissue models appropriate to the treatment of human breast tissue by using cw Nd:YAG laser radiation delivered with a interstitial fiber optic probe with a quartz diffusing tip, were recorded with an array of fifteen 23-gauge needle thermocouple probes connected to a laboratory computer-based data acquisition system. RESULTS: By using a stepwise decreasing power cycle to avoid tissue charring, acceptably symmetric thermal fields of repeatable volumetric dimensions were obtained. Reproducible thermal gradients and predictable tissue necrosis without carbonization could be induced in a 3-cm-diameter region around the fiber probe during a single treatment lasting only 3 minutes. The time-dependences of the temperature rise of the thermocouples surrounding the LITT probe were quantitatively modeled with simple linear functions during the applied laser heating cycles. CONCLUSION: Analysis of our experimental results show that reproducible, symmetric and predictable volumetric temperature increases in time can be reliably produced by interstitial laser thermotherapy.

Adipose Tissue↗
PubMed2000

Thermal unbinding of highly oriented phospholipid membranes.

We present a temperature dependent x-ray reflectivity study of highly oriented, fully hydrated multilamellar phospholipid membranes. Both the specular and diffuse (nonspecular) x-ray reflectivity were measured for dimyristoyl-sn-glycero-phosphocholine (DMPC) and oleoyl-palmitoyl-sn-glycero-phosphocholine (POPC) on silicon substrates in excess water. In this configuration the repeat distance as well as the fluctuation spectra can be determined as a function of temperature. Both model systems studied exhibit a discontinuous unbinding transition from a substrate bound, multilamellar state to a state of freely dispersed bilayers in water. In the unbound phase a single membrane remains on the substrate.

Dimyristoylphosphatidylcholine↗
PubMed1999

Spontaneous Thermal Convection in the Vicinity of Electrolyte/Water Interfaces.

We present theoretical evidence for transient roll-cell convection induced in the vicinity of freshly prepared electrolyte/water interfaces. The mechanism relies on a hitherto unrecognized type of double-diffusive convection. Electrolyte diffusion down the strong concentration gradient at the interface produces local heating just below the interface as the electrolyte becomes more dilute. If the concentration gradient at the interface is sufficiently large, temperature gradients on the order of one Kelvin per centimeter can be induced by this mechanism. We assume the horizontal electrolyte/water interface is contained in a long prism with a square vertical cross section and that the electrolyte solution is denser than the supernatant water layer. Provided that the sidewalls of the prism are thermally conducting, convection commences at the junction of the interface (at half the height of the square section) and these walls. In each vertical semi-cross-section, two roll cells evolve at the interface and the lower cell rapidly gains intensity at the expense of the counter-rotating upper cell. After a short period of time the lower cell migrates diagonally downward to lie just beneath the interface and the associated region of local heating. Although the fluid velocities associated with this roll cell initially increase with time, they do not appear to be sufficiently strong to distort the vertical stratification of the electrolyte's concentration profile. In a cylindrical annulus standing on its circular base the dominant roll cell takes the form of a toroidal vortex resembling a Taylor vortex. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Effect of thermal injury with Pseudomonas aeruginosa infection on pulmonary and systemic bacterial clearance.

BACKGROUND: Despite improvements in burn wound care, infections, particularly pneumonia, remain a major hurdle to recovery from thermal injury. After burns, a variety of systemic immune and inflammatory changes contribute to the risk of infection. Clinically, infection coupled with burn injury seems to adversely affect susceptibility to subsequent infection. METHODS: Using a mouse model of 10% total body surface area, full-thickness, third-degree burns with quantitative bacterial cultures of multiple tissues, the effect of graded intratracheal and intraperitoneal infections with Pseudomonas aeruginosa on the development of infection was assessed. RESULTS: P. aeruginosa infection of blood and lung were demonstrated in burned mice 4 hours after they received 1 to 7.2x10(5) P. aeruginosa intratracheally but not in unburned control mice. Disseminated infection from endogenous bacterial species (Proteus, Enterococcus, Streptococcus) involving the lungs, liver, blood, and subeschar space was observed in mice that received both burns and infection with P. aeruginosa (intraperitoneally and intratracheally) but not with infection or burn alone (p<0.01). After burns, pulmonary bacterial clearance was delayed in association with both pulmonary infection (7.2x10(5) P. aeruginosa intratracheally) and intraperitoneal infection (10(7) P. aeruginosa intraperitoneally). Histologically, diffuse pneumonitis was observed in mice that received burns and infection but not in mice with either infection or burns alone. CONCLUSION: Small thermal injuries coupled with transient infection of the lungs or peritoneum delay the clearance of bacteria from the lungs and contribute to infection of the lungs, liver, burn site, and blood by endogenous organisms. These studies support the synergy of relatively small thermal injuries with infectious exposures in the pathogenesis of pneumonia and systemic infections after burns.

Animals↗
PubMed1997

Comparison of 810 nm and 1064 nm wavelengths for interstitial laser photocoagulation in rabbit brain.

BACKGROUND AND OBJECTIVE: This laboratory animal study is a comparison of Nd:YAG 1064 nm and diode 810 nm laser wavelengths in brain interstitial laser photocoagulation (ILP). Specific goals were to identify potential complications and physical characteristics of the thermal damage at both wavelengths prior to undertaking a clinical trial in humans. STUDY DESIGN/MATERIALS AND METHODS: A total of 41 ILP illuminations were performed in vivo in the brains of 33 anesthetized rabbits using plane-cut fiber tips implanted directly or through catheters, and diffusing fiber tips. Delivered powers ranged from 1.1 to 4.2 W. Exposures ranged from 300 to 900 s. Survival ranged from 0 to 48 h. Experiments were performed in animals with and without VX-2 brain tumors. RESULTS: Thermal damage from 1.1 W at 810 nm was similar to that from 1.6 W at 1064 nm, but more pronounced. With plane-cut fiber tips, there was a greater propensity for severe physical effects (smoke, charring, bubbling, surface damage) at 810 nm than at 1064 nm, yet hemorrhage, thrombosis and vapor dissemination were observed at both wavelengths, in both normal brain and tumor. CONCLUSIONS: For ILP in brain, 1064 nm may be better suited than 810 nm, although both are questionable with plane-cut-fiber tips. Compactness and portability may be the only valid reasons for using laser diodes operating around 810 nm. At 1064 nm, the power delivered from plane-cut fiber tips should be less than 1.5 W, necessitating long exposures, or else an open catheter should be used. Fiber tips with distributed emission may be preferred, provided structural integrity can be maintained.

Animals↗
PubMed2005

Classical and quantum diffusion in the presence of velocity-dependent coupling.

A generalized system-plus-reservoir model is introduced, which includes four kinds of couplings between the coordinates and velocities of a system and its environment. It is found that the velocity-dependent coupling is not equivalent to a coordinate coupling due to the different power spectra of thermal noise. Harmonic velocity and acceleration noises are proposed which correspond to the coordinate-velocities and velocity-velocities couplings, respectively, if the environmental oscillators are assumed to have a harmonic spectral distribution. Indeed, the velocity-dependent coupling can induce ballistic diffusion of a force-free particle and the mean square velocity depends on the initial preparation. Quantum ballistic diffusion is also presented and its velocity correlation function is found to be unstable at any time. One of real examples of velocity-coordinates coupling is a one-electron atom interacting with the radiation field. A particle moving in a periodic potential shows a nonergodic behavior.

Journal Article↗
PubMed1999

Silicon nitride coating on titanium to enable titanium-ceramic bonding.

Failures that occur in titanium-ceramic restorations are of concern to clinicians. The formation of poorly adhering oxide on titanium at dental porcelain sintering temperatures causes adherence problems between titanium and porcelain, which is the main limiting factor in the fabrication of titanium-ceramic restorations. To overcome this problem a 1-microm thick Si3N4 coating was applied to a titanium surface using a plasma-immersion implantation and deposition method. Such a coating serves as an oxygen diffusion barrier on titanium during the porcelain firings. The protective coating was characterized in the as-deposited condition and after thermal cycling. Cross sections of Ti/Si3N4-porcelain interface regions were examined by various electron microscopy methods and by energy dispersive analysis of X-rays to study the Si3N4 film's effectiveness in preventing titanium oxidation and in forming a bond with porcelain. The experiments have shown that this Si3N4 coating enables significant improvement in Ti-ceramic bonding.

Dental Porcelain↗
PubMed2005

Simultaneous monitoring of temperature and T1: methods and preliminary results of application to drug delivery using thermosensitive liposomes.

A method is presented to obtain temperature and longitudinal relaxivity measurements simultaneously and in near real-time. Quantitative relaxivity values are obtained from the signal magnitude from fast Look-Locker EPI data, whereas phase information from all signal samples on the recovery curve is combined to provide temperature values using the proton resonance frequency method. The utility of this technique is illustrated in an in vitro experiment with thermosensitive liposomes, which are studied as potential micro vehicles for local drug delivery. The method allowed measuring the evolution of relaxivity during RF-heating of liposomes containing a paramagnetic contrast agent, demonstrating increase of liposome permeability near the phase transition temperature. Potential applications are monitoring of local drug delivery using thermosensitive liposomes, and confirmation of reaching the liposomes' threshold temperature during thermal therapy.

Diffusion↗
PubMed1993

A near perfect temperature adaptation of bilayer order in vertebrate brain membranes.

The bilayer order of a brain synaptic membrane fraction from a number of fish, mammalian and avian species have been compared in relation to their respective body temperatures using steady-state and time-resolved fluorescence anisotropy techniques. Fluorescence anisotropy for both 1,6-diphenyl-1,3,5-hexatriene and trans-parinaric acid increased in the order: antarctic Notothenia, trout, perch, cichlid, rat and starling, this also being the order of increasing body temperature. This suggests that cold-adapted fish species possess more disordered brain membranes than warm-adapted fish species, and mammals and birds membranes were more ordered than fish membranes. Comparison of temperature profiles for both fluorescence probes showed that fish species display similar anisotropies, and by inference bilayer order, to mammals and birds when measured at their respective body temperatures. Time-resolved analysis showed that the interspecific differences in (P2) order parameter was consistently related to body temperature whilst the rotational diffusion coefficient was not. These results suggest that brain membrane order is highly conserved within the vertebrates despite large differences in thermal habits and phylogenetic position. Polar fish species have by far the lowest bilayer order indicating that invasion of extreme cold habitats involved an adaptive decrease in bilayer order and conversely adoption of a high body temperature by mammals involved an adaptive increase in bilayer order. The conservation of membrane static order for these species at their respective body temperatures indicates a regulatory control of this aspect of membrane hydrocarbon structure and the functional importance of this structure.

Adaptation, Physiological↗
PubMed1980

Laminates of poly(2-hydroxyethyl methacrylate) and polybutadiene as potential burn covering.

The preparation and the physical characterization of poly(2-hydroxyethyl methacrylate) thermally grafted onto polybutadiene (PHEMA/PB) are reported. The presence of polybutadiene increases the tensile properties of the film and prevents water diffusion through it while it does not affect the oxygen permeability of the PHEMA. The potential use of this material as burn wound cover is suggested.

Bandages↗
PubMed2004

Albumin loaded microsphere of amphiphilic poly(ethylene glycol)/ poly(alpha-ester) multiblock copolymer.

The purpose of this study is to investigate the microspheres (MS) based on (AB)(n) type amphiphilic multiblock copolymers for sustained and complete release of a model protein, bovine serum albumin (BSA). The MS were prepared by a modified water-in-oil-in-water (W/O/W) double emulsion method using amphiphilic multiblock copolymers consisting of poly(ethylene glycol) (PEG) and a poly(alpha-ester), poly(epsilon-caprolactone) (PCL) or poly(l-lactic acid) (PLLA). The size of MS and encapsulation efficiency of BSA within MS were not noticeably influenced by the copolymer composition used in this experiment. While BSA was completely released from PEG/PLLA MS through matrix erosion and the diffusion of BSA, it was released only to an extent of 60% from PEG/PCL MS solely through the diffusion process. However, the release of BSA from PEG/PCL MS dramatically increased and then reached 100% release in 10 days after thermal treatment of the MS at 50 degrees C for 30 min in the middle of release test (on day 15).

Delayed-Action Preparations↗