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Results for “Thermal Diffusion”

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PubMed2005

Experimental studies of the vapor phase nucleation of refractory compounds. VI. The condensation of sodium.

In this paper we discuss the condensation of sodium vapor and the formation of a sodium aerosol as it occurs in a gas evaporation condensation chamber. A one-dimensional model describing the vapor transport to the vapor/aerosol interface was employed to determine the onset supersaturation, in which we assume the observed location of the interface is coincident with a nucleation rate maximum. We then present and discuss the resulting nucleation onset supersaturation data within the context of nucleation theory based on the liquid droplet model. Nucleation results appear to be consistent with a cesium vapor-to-liquid nucleation study performed in a thermal diffusion cloud chamber.

Journal Article↗

PubMed2006

Atomistic simulations of shock-induced alloying reactions in Ni/Al nanolaminates.

We employ molecular dynamics simulations with a first principles-based many body potential to characterize the exothermic alloying reactions of nanostructured Ni/Al multilayers induced by shock loading. We introduce a novel technique that captures both the initial shock transit as well as the subsequent longer-time-scale Ni3Al alloy formation. Initially, the softer Al layers are shock heated to a higher temperature than the harder Ni layers as a result of a series of shock reflections from the impedance-mismatched interfaces. Once initiated, the highly exothermic alloying reactions can propagate in a self-sustained manner by mass and thermal diffusion. We also characterize the role of voids on the initiation of alloying. The interaction of the shock wave with the voids leads not only to significant local heating (hot spots) but also directly aids the intermixing between Al and Ni; both of these phenomena contribute to a significant acceleration of the alloying reactions.

Journal Article↗

PubMed2000

Elucidating the pulsed-dye laser treatment of sebaceous hyperplasia in vivo with real-time confocal scanning laser microscopy.

BACKGROUND: Several case reports document successful treatment of sebaceous hyperplasia with the pulsed-dye laser. Moreover, noninvasive real-time confocal laser scanning microscopy elucidates the vascular nature of these lesions and their pathophysiologic response to treatment mediated by vessel coagulation. METHODS: Ten patients with 29 lesions of sebaceous hyperplasia were treated with 3 stacked 5-mm pulses of the 585-nm pulsed-dye laser at fluences of 7 or 7.5 J/cm(2). Confocal imaging was performed before and immediately after treatment, as well as at 2, 4, and 8 weeks of follow-up. RESULTS: The great majority of lesions responded to one treatment, with complete disappearance in 28%, decrease in diameter in 66%, and flattening in 93%. Although 28% recrudesced after initial involution, only 7% recurred completely. Three lesions became eroded or crusted, and 7 experienced cutaneous depressions before complete healing, but no scarring or pigmentary side effects were noted. Confocal imaging revealed a prominent "crown" of blood vessels surrounding the sebaceous duct and coagulation of these vessels with pulsed-dye laser treatment. However, the vessels reappeared during follow-up, and no noticeable morphologic changes in the sebaceous duct were noted. CONCLUSION: Vascular targeting of sebaceous hyperplasia can be monitored with real-time reflectance confocal microscopy. Most sebaceous hyperplasia regresses after one treatment with 3 stacked pulses of the 585-nm pulsed-dye laser. Whether this response is due to temporary ischemia induced by selective vessel destruction or nonspecific thermal diffusion beyond the vessels from pulse stacking has not been determined.

Adult↗

PubMed2003

Supplemental perioperative fluid administration increases tissue oxygen pressure.

BACKGROUND: Wound infections are common and serious surgical complications. Wound perfusion delivers oxygen, inflammatory cells, growth factors, and cytokines to injured tissues. Hypoperfused regions experience low oxygen tensions that do not support adequate oxidative killing or wound healing. Clinicians may fail to recognize clinically important hypovolemia because hemodynamic stability and urine output are maintained after peripheral perfusion is compromised. We tested the hypothesis that supplemental fluid administration during and after elective colon resection increases tissue perfusion and tissue oxygen pressure. METHODS: Fifty-six patients undergoing colon resection were randomly assigned to conservative (8 mL x kg(-1) x h(-1), n = 26) or aggressive (16 to 18 mL x kg(-1) x h(-1), n = 30) fluid management. Anesthetic technique was standardized. We used 60% nitrous oxide in 40% oxygen. During surgery and postanesthetic recovery, subcutaneous oxygen tension (P(sq)O(2)) was measured by using a polarographic sensor implanted subcutaneously into 1 upper arm. Capillary blood flow was evaluated postoperatively with a thermal diffusion system. Data were analyzed with 2-tailed t tests; P value less than.05 was considered statistically significant. RESULTS: Hemodynamic and renal responses were similar in the groups. Intraoperative tissue oxygen tension was significantly greater in patients given supplemental fluid: 81 +/- 26 vs 67 +/- 18 mm Hg, P =.03. Postoperative P(sq)O(2) (77 +/- 26 vs 59 +/- 15 mm Hg, P =.009) and capillary blood flow (69 +/- 12 vs 53 +/- 12, P <.001) were also greater in the supplemental fluid patients. CONCLUSIONS: Supplemental perioperative fluid administration significantly increases tissue perfusion and tissue oxygen partial pressure. Optimizing tissue perfusion will require providing more fluid than indicated by normal clinical criteria or use of invasive monitoring to guide treatment. The actual effect of supplemental fluid administration on incidence of wound infection requires further investigation.

Adult↗

PubMed1995

Order and disorder in fluid motion.

The development of complex states of fluid motion is illustrated by reviewing a series of experiments, emphasizing film flows, surface waves, and thermal convection. In one dimension, cellular patterns bifurcate to states of spatiotemporal chaos. In two dimensions, even ordered patterns can be surprisingly intricate when quasiperiodic patterns are included. Spatiotemporal chaos is best characterized statistically, and methods for doing so are evolving. Transport and mixing phenomena can also lead to spatial complexity, but the degree depends on the significance of molecular or thermal diffusion.

Journal Article↗

PubMed1990

Postoperative monitoring of cerebral blood flow in patients harboring intracranial aneurysms.

Fifteen patients harbouring intracranial aneurysms were monitored postoperatively. A thermal diffusion flow probe was placed on the cortex, in an area of interest, and continuous recording of cerebral blood flow (CBF) was carried out for 1-4 days. Vasospasm can also be detected by clinical deterioration, increased velocity by transcranial Doppler, and by angiographical evidence of decrease in vessel calibre. A comparison was made between these methods of determining vasospasm and changes in CBF. Three patients had unruptured aneurysms and no evidence of vasospasm. These patients had a range of CBF from 44 to 100 cc 100 g-1 min-1 with a daily mean of 78 cc 100 g-1 min-1. One patient was operated on, in a delayed fashion, after a period of vasospasm on post-subarachnoid haemorrhage (SAH) Day 18 and was found to have a CBF of 40 cc 100 g-1 min-1 when the pCO2 was 21 Torr and the mean blood pressure (BP) was 99 Torr. The development of vasospasm was correlated with a CBF of less than 40 cc 100 g-1 min-1. Some patients with vasospasm also develop a significant drop in CBF during the period of monitoring. Using these criteria, CBF monitoring predicted the development of vasospasm in seven patients, was compatible with the clinical course in three patients and was misleading in two patients. In the seven patients in which CBF predicted vasospasm, changes were seen in CBF prior to changes observed by clinical examination, transcranial Doppler, and/or angiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Angiography↗

PubMed2004

Infrared thermographic SAR measurements of interstitial hyperthermia applicators: errors due to thermal conduction and convection.

Thermal conduction and convection were examined as sources of error in thermographically measured SAR patterns of an interstitial microwave hyperthermia applicator. Measurements were performed in a layered block of muscle-equivalent phantom material using an infrared thermographic technique with varying heating duration. There was a 52.7% reduction in maximum SAR and 75.5% increase in 50% iso-SAR contour area for a 60-s heating duration relative to a 10-s heating duration. A finite element model of heat transfer in an homogeneous medium was used to model conductive and convective heat transfer during the thermographic measurement. Thermal conduction artefacts were found to significantly distort thermographically measured SAR patterns. Convective cooling, which occurs when phantom layers are exposed for thermal image acquisition, was found to significantly affect the magnitude, but not the spatial distribution, of thermographically measured SAR patterns. Results from this investigation suggest that the thermal diffusion artefacts can be minimized if the duration of the applied power pulse is restricted to 10 s or less.

Hot Temperature↗

PubMed1985

Release of arsenic from semiconductor wafers.

The production of integrated circuits and other semiconductor devices requires the introduction of impurities or dopants into the crystal lattice of a silicon substrate. This "doping" or junction formation is achieved through one of two processes: thermal diffusion or ion implantation. Ion implantation, the more contemporary and more accurate of the two processes, accomplishes junction formation by bombarding selected areas of the silicon wafer with a beam of dopant ions. Inorganic arsenic, which is regulated by the Occupational Health and Safety Administration (OSHA) as a carcinogen, is frequently used as dopant material. Silicon wafers are found to emit inorganic arsenic following ion implantation. Data collected during this experiment demonstrate that arsenic is released over a 3.5-hour period following implantation and that the total amount of arsenic emitted may approach 6.0 micrograms per 100 wafers processed within 4 hours after implantation. The discovery and quantification of this phenomenon suggest that newly implanted silicon wafers are a potential source of arsenic contamination--a source that may impact both the quality of the work environment and the integrated circuit product.

Air Pollutants, Occupational↗

PubMed2000

Chandra Uncovers a Hidden Low-Luminosity Active Galactic Nucleus in the Radio Galaxy Hydra A (3C 218).

We report the detection with Chandra of a low-luminosity active galactic nucleus (LLAGN) in the low-ionization nuclear emission-line region (LINER) hosted by Hydra A, a nearby (z=0.0537) powerful FR I radio galaxy with complex radio and optical morphology. In a 20 ks ACIS-S exposure during the calibration phase of the instrument, a point source is detected at energies greater, similar2 keV at the position of the compact radio core, embedded in diffuse thermal X-ray emission (kT approximately 1 keV) at softer energies. The spectrum of the point source is well fitted by a heavily absorbed power law with intrinsic column density NintH approximately 3x1022 cm-2 and photon index Gamma approximately 1.7. The intrinsic (absorption-corrected) luminosity is L2-10keV approximately 1.3x1042 ergs s-1. These results provide strong evidence that an obscured AGN is present in the nuclear region of Hydra A. We infer that the optical/UV emission of the AGN is mostly hidden by the heavy intrinsic reddening. In order to balance the photon budget of the nebula, we must either postulate that the ionizing spectrum includes a UV bump or invoke and additional power source (shocks in the cooling flow or interaction with the radio jets). Using an indirect estimate of the black hole mass and the X-ray luminosity, we infer that the accretion rate is low, suggesting that the accretion flow is advection dominated. Finally, our results support current unification schemes for radio-loud sources, in particular the presence of the putative molecular torus in FR I galaxies. These observations underscore the power of the X-rays and of Chandra in the quest for black holes.

Journal Article↗

PubMed2000

Physical properties of hydrated tissue determined by surface interferometry of laser-induced thermoelastic deformation.

Knee meniscus is a hydrated tissue; it is a fibrocartilage of the knee joint composed primarily of water. We present results of interferometric surface monitoring by which we measure physical properties of human knee meniscal cartilage. The physical response of biological tissue to a short laser pulse is primarily thermomechanical. When the pulse is shorter than characteristic times (thermal diffusion time and acoustic relaxation time) stresses build and propagate as acoustic waves in the tissue. The tissue responds to the laser-induced stress by thermoelastic expansion. Solving the thermoelastic wave equation numerically predicts the correct laser-induced expansion. By comparing theory with experimental data, we can obtain the longitudinal speed of sound, the effective optical penetration depth and the Grüneisen coefficient. This study yields information about the laser tissue interaction and determines properties of the meniscus samples that could be used as diagnostic parameters.

Elasticity↗

PubMed2004

Reflux drying of aerosols.

The goal of our efforts has been to generate high aerosolized drug concentrations, so that the entire inhaled dose may be delivered to the animal in a relatively short time interval, typically one minute or less. In this report, we have examined the use of a reflux condenser coupled with an external heat source as a means to dry aerosol particles. The specific interest was to examine the parameters influencing the drying process and identify practical experimental conditions that would allow drying of aerosol particles. Aqueous solutions of cesium chloride were atomized with an ultrasonic driver, and the resulting cloud was subsequently passed through an externally heated column with an inner condenser cooled with flowing water. Increasing the airflow rate increased the output of total mass(water + CsCl) but decreased the particle transit efficiency. At a constant airflow rate, decreasing the wall-to-condenser temperature ratio led to a progressive increase in particle loss, but a maximum was observed in the water removal efficiency. While thermal diffusion and the thermophoretic effect may have an impact on the drying process, non-steady state conditions, convective currents, inertial impaction, turbulence, and changes in the condenser boundary layer are likely to have a role in particle drying. In spite of the numerous complexities, practical operating conditions were identified for efficient particle drying with high dry mass transit efficiency.

Aerosols↗

PubMed2001

New scheme for calculation of annular dark-field STEM image including both elastically diffracted and TDS waves.

A new scheme of calculation of high-angle annular dark-field STEM image, capable of including both elastically diffracted and thermal diffuse scattering waves, has been presented by a combination of Pennycook's and Nakamura's methods. The new scheme has been demonstrated for image simulations of Si(011) as functions of thickness, defocus values and detector angles. In the present method, the TDS electron intensities are treated in the same way as in Pennycook's method, having a clear physical picture of its origin and reflecting the atom configuration in the systems. For the case of Si(011), it has been confirmed that at the detector angle of 60 to 160 mrad, which is usually applied, the image becomes highly incoherent, and even the image formed only from SOLZ beams becomes incoherent at the detector angle. At a low detector angle, however, the image has coherent features indicating the necessity of a simulation for individual systems.

Journal Article↗

PubMed2001

Prospects of atomic resolution imaging with an aberration-corrected STEM.

We investigated high-resolution scanning transmission electron microscope (STEM) images obtained from a microscope equipped with a spherical aberration corrector. The probe size (full-width at half-maximum) is reduced to 0.76 A at 200 kV by assuming the fifth-order spherical aberration coefficient C5 = 100 mm. For the simulation we have used the recently developed scheme for a STEM image simulation based on the Fast Fourier Transform (FFT) multislice algorithm. The peak-to-background (P/B) ratio of the high-angle annular dark-field (HAADF) image is significantly improved at a thin specimen region. Although the P/B ratio becomes worse at a thicker region, the resolution is kept high even at such a region. An almost true HAADF signal will be obtained even from a weak-scattering phosphorous column in InP [001] when the background is subtracted. In the bright-field image the coherent character of elastic scattering is suppressed by averaging over a large convergence angle, making the specimen effectively self-luminous. The claim that HAADF imaging is relatively insensitive to a defocus as well as a specimen thickness is valid only qualitatively, and a detailed image simulation will be required for a quantitative analysis as in the case of the conventional transmission electron microscope. It was noted that the delta function approximation for the object function may not be applicable for a very fine probe, and that the achievable resolution of the HAADF imaging will be limited by the widths of the high-angle thermal diffuse scattering potential.

Journal Article↗

PubMed2001

Artificial bright spots in atomic-resolution high-angle annular dark field STEM images.

Artificial bright spots, which appear in some atomic resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) images, have been accounted for by simulations based on Bloch wave description. This is illustrated with Si and SrTiO3 images. The simulation reveals that bright spots on no-atomic columns in [011]-orientated Si images are produced by thermal diffuse scattering from Si atoms on their surrounding atomic columns, which are under the subsidiary peaks in the incident convergent electron probe. Similarly, bright spots on oxygen columns in [001]-orientated SrTiO3 images are ascribed to Sr and Ti atoms in their surrounding atomic columns rather than O atoms in the O columns. The probe function, therefore, provides a simple explanation for the appearance of these artificial spots.

Journal Article↗

PubMed2004

Different impact of normo- and hypotensive brain death on renal macro- and microperfusion--an experimental evaluation in a porcine model.

BACKGROUND: Despite the growing use of kidneys from living donors, organs harvested from brain dead donors are the dominant graft types used in renal transplantation. It is accepted that brain death (BD) has a damaging effect on the renal allograft, with a lower graft survival. Amongst various causes, changes in renal microperfusion could be responsible. Renocortical microperfusion was assessed during BD using thermal diffusion in a porcine model. METHODS: Two types of BD were induced in two groups of pigs [hypotension (Hypo-BD): n = 11; normotension (Normo-BD): n = 10] and compared to controls (n = 5) over a period of 210 min. We analysed systemic parameters [heart rate (HR), mean arterial blood pressure (MAP)], aortic blood flow (ABF) and renal perfusion [renal artery blood flow (RABF) and renocortical blood flow (RCBF)]. RESULTS: Following the two distinct forms of BD induction, a stable normo- or hypotension was observed. Haemodynamic parameters were only slightly changed (control group: MAP, 62+/-2 mmHg; HR, 95+/-3/min; Normo-BD: MAP, 56+/-4 mmHg; HR, 104+/-8/min; Hypo-BD: MAP, 43+/-3 mmHg; HR, 112+/-7/min). Solely dependent on systemic haemodynamics, RABF and RCBF decreased in the Hypo-BD (RABF: 142+/-19 to 94+/-9 ml/100 g/min; RCBF: 80+/-4 to 52+/-2 ml/100 g/min), while in Normo-BD group RABF mildly changed (158+/-13 ml/100 g/min) and RCBF decreased slightly from 76+/-3 to 70+/-6 ml/100 g/min. As opposed to the Normo-BD group, animals with Hypo-BD showed a significant decrease in RABF (reduction of 34%) and RCBF (reduction of 35%) with a sharp drop of MAP (reduction of 25%), however ABF remained relatively constant. CONCLUSIONS: In this model, a reduction of renocortical microperfusion in brain dead pigs was only found during haemodynamic instability (hypotension) and could not be attributed to BD as such. Our findings would support intensive cardiocirculatory stabilization for potential BD donors in order to minimize kidney preservation damage.

Animals↗

PubMed1996

Strangulation injuries in children. Part 2. Cerebrovascular hemodynamics.

The cerebrovascular hemodynamics were recorded in two children with comparable hypoxic-ischemic injuries after strangulation. Monitoring was initiated within 13 hours of injury and continued for at least 38 hours. The profile included continuous measurements of cortical regional cerebral blood flow (rCBF) with a subdural thermal diffusion probe, intracranial pressure, mean arterial pressure, and expired CO2 tension. Data sets were obtained every 15 minutes or every 5 minutes during epochs of hyperventilation and inotropic support. Arterial CO2 and oxygen content and pH and, in the second patient, cardiac output (and cardiac index) were determined every 3 to 6 hours. Both children showed cortical hyperemia with a gradual rise of rCBF during the study; neither child showed elevated intracranial pressure. Mean CO2 reactivities were 1.8 and 2.1 mL/100 g/minute/mm Hg, with gradual elevations during the study. Mean cerebrovascular resistances were 0.7 and 0.9 mL/100 g/minute/mm Hg, respectively. Dissociative vasoparalysis with loss of autoregulation and preservation of CO2 reactivity was observed in both children. In the second child, during two periods of hyperventilation, an inverse steal occurred with rCBF indirectly related to expired CO2 tension; the rCBF was not related to changes in cardiac output or cardiac index. Neurologic outcome was not related to mean levels of rCBF, CPP, and CO2 reactivity, or clinical dissociative vasoparalysis. Lower initial and mean values of rCBF and an inverse steal after hyperventilation were associated with a poor outcome in the second patient.

Adolescent↗

PubMed1991

Continuous regional cerebral blood flow monitoring in acute craniocerebral trauma.

Regional cortical cerebral blood flow (rCBF) and intracranial pressure (ICP) were monitored continuously with a combined thermal diffusion probe/ICP monitor in 12 patients (8 men and 4 women; mean age, 31 years; range, 7-65 years) with acute head injuries. The mean Glasgow Coma Scale score at admission was 6 (range, 4-12). The rCBF/ICP probes were placed during surgical procedures (n = 11) or in an intensive care unit (n = 1) for subdural hematomas (n = 7), cerebral contusions (n = 4), and an epidural hematoma (n = 1). No probe-related complications occurred. Reduced CBF often occurred and was often inversely proportional to elevations in ICP. Posttraumatic cerebral arterial vasospasm in one patient was detected by rCBF monitoring and confirmed by angiography. In 6 patients who progressed to brain death, rCBF patterns disappeared, which correlated with their clinical and electroencephalographic examinations. Several patients with severe, diffuse brain injuries and high ICP had hyperemic rCBF patterns. In 2 of these patients, increases in rCBF preceded rises in ICP, which implied loss of autoregulation as a mechanism in the development of malignant cerebral edema. This method of CBF monitoring has not yet been established for clinical decision making. The early detection of ischemic or hyperemic responses by continuous CBF monitoring could hasten intervention aimed at restoring adequate tissue perfusion. The technique could also serve as an index of the efficacy of therapeutic interventions and is suitable to gain more insight into the pathophysiology of head injury, especially the relationship of CBF to ICP.

Adolescent↗

PubMed2001

Carbon dioxide reactivity and pressure autoregulation of brain tissue oxygen.

OBJECTIVE: To describe the normal relationships between brain tissue oxygen tension (PbrO2) and physiological parameters of systemic blood pressure and CO2 concentrations. METHODS: Licox Clark-type oxygen probes (GMS mbH, Kiel, Germany) were inserted in the frontal white matter of 12 swine maintained under general anesthesia with a 1.0 fraction of inspired oxygen (FiO2). In seven swine, alterations in end-tidal carbon dioxide (ET-CO2) concentration (range, 13-72 mm Hg) were induced via hyperventilation or instillation of CO2 into the ventilation circuit. In nine swine, mean arterial pressure (MAP) (range, 33-200 mm Hg) was altered; phenylephrine was used to induce hypertension, and a nitroprusside-esmolol combination or systemic hemorrhage was used for hypotension. Quantitative cerebral blood flow (CBF) was measured in two animals by using a thermal diffusion probe. RESULTS: Mean baseline PbrO2 was 41.9 +/- 11.3 mm Hg. PbrO2 varied linearly with changes in ET-CO2, ranging from 20 to 60 mm Hg (r2 = 0.70). The minimum PbrO2 with hypocarbia was 5.9 mm Hg, and the maximum PbrO2 with hypercarbia was 132.4 mm Hg. PbrO2 varied with MAP in a sigmoid fashion suggestive of pressure autoregulation between 60 and 150 mm Hg (r2 = 0.72). The minimum PbrO2 with hypotension was 1.4 mm Hg, and the maximum PbrO2 with hypertension was 97.2 mm Hg. In addition, CBF correlated linearly with PbrO2 during CO2 reactivity testing (r2 = 0.84). CONCLUSION: In the uninjured brain, PbrO2 exhibits CO2 reactivity and pressure autoregulation. The relationship of PbrO2 with ET-CO2 and MAP appears to be similar to those historically established for CBF with ET-CO2 and MAP. This suggests that, under normal conditions, PbrO2 is strongly influenced by factors that regulate CBF.

Animals↗