Overpressure—elevated hydrostatic pressure—was used to assess the role of gas or vapor bubbles in distorting the shape and position of a high-intensity focused ultrasound (HIFU) lesion in tissue. The ...shift from a cigar-shaped lesion to a tadpole-shaped lesion can mean that the wrong area is treated. Overpressure minimizes bubbles and bubble activity by dissolving gas bubbles, restricting bubble oscillation and raising the boiling temperature. Therefore, comparison with and without overpressure is a tool to assess the role of bubbles. Dissolution rates, bubble dynamics and boiling temperatures were determined as functions of pressure. Experiments were made first in a low-overpressure chamber (0.7 MPa maximum) that permitted imaging by B-mode ultrasound (US). Pieces of excised beef liver (8 cm thick) were treated in the chamber with 3.5 MHz for 1 to 7 s (50% duty cycle).
In situ intensities (I
SP) were 600 to 3000 W/cm
2. B-mode US imaging detected a hyperechoic region at the HIFU treatment site. The dissipation of this hyperechoic region following HIFU cessation corresponded well with calculated bubble dissolution rates; thus, suggesting that bubbles were present. Lesion shape was then tested in a high-pressure chamber. Intensities were 1300 and 1750 W/cm
2 ( ± 20%) at 1 MHz for 30 s. Hydrostatic pressures were 0.1 or 5.6 MPa. At 1300 W/cm
2, lesions were cigar-shaped, and no difference was observed between lesions formed with or without overpressure. At 1750 W/cm
2, lesions formed with no overpressure were tadpole-shaped, but lesions formed with high overpressure (5.6 MPa) remained cigar-shaped. Data support the hypothesis that bubbles contribute to the lesion distortion. (E-mail: bailey@apl.washington.edu)
This cross-sectional school-based study explored the relationship between adolescent use of cigarettes and marijuana and the sensation seeking personality factors of (1) Disinhibition and (2) Thrill ...and Adventure Seeking. The study population included a representative sample of both male and female 8th and 11th graders in the state of Delaware. Analytic methods utilized included correlational analysis and multivariate logistic regression. In the multivariate logistic regression models, the Disinhibition personality factor accounted for cigarette and marijuana using behaviors with odds ratios ranging between 2 and 3. Thrill and Adventure Seeking was not a significant explanatory variable in any of the final multivariate models. Potential confounders (age, gender and race) were considered in all analyses. Of all the two-way interactions assessed, none was significant. The findings from this study utilizing a large general community sample indicate that sensation seeking needs are a potential risk factor for adolescent substance use.
Using human whole blood samples with and without contrast agent (CA), we evaluated the effect of exposures to focused, continuous wave (CW) 1.1-MHz ultrasound for durations of 10 ms to 1 s at spatial ...average intensities of 560 to 2360 W/cm2. Cavitation was monitored with a passive cavitation detector and hemolysis was determined with spectroscopy. In whole blood alone, no significant cavitation, heating or hemolysis was detected at any exposure condition. Conversely, cavitation and hemolysis, but not heating, were detected in whole blood with CA. A CA concentration as low as 0.28 μL CA per mL whole blood at an intensity of 2360 W/cm2 for 1 s resulted in measurable cavitation and a 6-fold increase in hemolysis compared to shams. Cavitation and hemolysis increased proportional to the concentration of CA and duration of exposure. In samples containing 4.2 μL CA per mL whole blood exposed for 1 s, a threshold was seen at 1750 W/cm2 where cavitation and hemolysis increased 10-fold compared to exposures at lower intensities. HIFU exposure of whole blood containing CA leads to significant hemolysis in vitro and may lead to clinically significant hemolysis in vivo.
A passive cavitation detector (PCD) identifies cavitation events by sensing acoustic emissions generated by the collapse of bubbles. In this work, a dual passive cavitation detector (dual PCD), ...consisting of a pair of orthogonal confocal receivers, is described for use in shock wave lithotripsy. Cavitation events are detected by both receivers and can be localized to within 5 mm by the nature of the small intersecting volume of the focal areas of the two receivers in association with a coincidence detection algorithm. A calibration technique, based on the impulse response of the transducer, was employed to estimate radiated pressures at collapse near the bubble. Results are presented for the in vitro cavitation fields of both a clinical and a research electrohydraulic lithotripter. The measured lifetime of the primary growth-and-collapse of the cavitation bubbles increased from 180 to 420 microseconds as the power setting was increased from 12 to 24 kV. The measured lifetime compared well with calculations based on the Gilmore-Akulichev formulation for bubble dynamics. The radiated acoustic pressure 10 mm from the collapsing cavitation bubble was measured to vary from 4 to 16 MPa with increasing power setting; although the trends agreed with calculations, the predicted values were four times larger than measured values. The axial length of the cavitation field correlated well with the 6-dB region of the acoustic field. However, the width of the cavitation field (10 mm) was significantly narrower than the acoustic field (25 mm) as bubbles appeared to be drawn to the acoustic axis during the collapse. The dual PCD also detected signals from "rebounds," secondary and tertiary growth-and-collapse cycles. The measured rebound time did not agree with calculations from the single-bubble model. The rebounds could be fitted to a Rayleigh collapse model by considering the entire bubble cloud as an effective single bubble. The results from the dual PCD agreed well with images from high-speed photography. The results indicate that single-bubble theory is sufficient to model lithotripsy cavitation dynamics up to time of the main collapse, but that upon collapse bubble cloud dynamics becomes important.
Travelers residing in communities having either small or medium-sized airports often avoid using the local airports in their regions, and use other (out-of-region) airports to take advantage of lower ...fares and more convenient airline services. This phenomenon is generally referred to as
airport leakage. Airport leakage can exist even in regions where the nearest substitute (airport) is over 150 miles away (i.e., in single-airport regions). This paper argues that airlines may have under-estimated the airport-leakage tendencies of travelers in single-airport regions, and consequently their current airfares in these regions may be higher than the optimal, or revenue-maximizing, levels. To test the validity of this argument, a simulation experiment was conducted by using the data for Des Moines International Airport (DSM), a medium airport serving the single-airport region in central Iowa (USA). The results imply that, for most airlines, current airfares in DSM may be higher than the optimal, and that they may increase revenues (or profits) by reducing airfares in DSM.
Using prospectively gathered data, we assessed whether depression is associated a risk for late-onset alcohol dependence, and whether that relationship differed by gender. The baseline interview was ...completed in 1981 (mean age
=
41.7 years, standard deviation (S.D.)
=
17.0, range 18–86) on a probability sample of Baltimore residents as part of the Epidemiologic Catchment Area Program. Between 1993 and 1996, the original cohort was traced (73% of the survivors were re-interviewed,
n
=
1920). Baseline depression items were subjected to gender-specific latent class analyses prior to exploring associations between class membership and two classifications of alcohol dependence: (1) lifetime prevalence, and (2) new onset assessed at follow-up. A depression syndrome class was identified (24% of the females and 20% of the males). The odds of lifetime alcohol dependence among those in the depressive syndrome class was significantly elevated for both sexes, relative to the non-depressed class. However, no appreciable association was found for depressive syndrome with the development of alcohol dependence. In this sample of middle-aged adults, the evidence supports an association for the presence of a depressive syndrome with lifetime alcohol dependence, but not for the new onset of alcohol dependence. Other predictors of alcohol dependence identified in the analyses are discussed.
There is strong evidence that cavitation bubble activity contributes to stone breakage and that shockwave-bubble interactions are involved in the tissue trauma associated with shockwave lithotripsy. ...Cavitation control may thus be a way to improve lithotripsy.
High-speed photography was used to analyze cavitation bubble activity at the surface of artificial and natural kidney stones during exposure to lithotripter shockwaves in vitro.
Numerous individual bubbles formed on the surfaces of stones, but these bubbles did not remain independent but rather combined to form clusters. Bubble clusters formed at the proximal and distal ends and at the sides of stones. Each cluster collapsed to a narrow point of impact. Collapse of the proximal cluster eroded the leading face of the stone, and the collapse of clusters at the sides of stones appeared to contribute to the growth of cracks. Collapse of the distal cluster caused minimal damage.
Cavitation-mediated damage to stones is attributable, not to the action of solitary bubbles, but to the growth and collapse of bubble clusters.
Predicting truck driver turnover Suzuki, Yoshinori; Crum, Michael R.; Pautsch, Gregory R.
Transportation research. Part E, Logistics and transportation review,
07/2009, Letnik:
45, Številka:
4
Journal Article
Recenzirano
We propose a decision tool for truckload carriers that can help control driver turnover rates. Our approach is to use an existing econometric method, along with the drivers’ work data, to predict the ...quit probability of each driver on a weekly basis, so that carriers can identify a subset of drivers who are “about to quit” in a timely manner. Empirical results from two case studies indicate that our approach does a nice job of predicting driver exits, and that it may become a useful management decision tool. Our method was recently adopted by two US truckload carriers.
To describe characteristics of general medical patients with suicidal ideation and to develop an efficient clinical strategy for identifying these patients.
Cross-sectional analysis of data without ...intervention.
A representative sample of community respondents interviewed as part of the National Institute of Mental Health Epidemiologic Catchment Area surveys.
A total of 6041 individuals who reported receiving care in general medical settings in the 6 months preceding the baseline interview.
Suicidal ideation within the year preceding the baseline interview.
A total of 154 patients (2.6%) had experienced suicidal thoughts within the previous year. In multivariate analyses, the following sociodemographic factors were significantly associated with having suicidal ideation: being white (odds ratio OR, 2.8; P < .001) relative to African American, separated or divorced (OR, 1.8; P = .03) relative to married, and aged 18 to 30 years (OR, 2.3; P = .02) or aged 31 to 50 years (OR, 2.1; P = .03) relative to those older than 65 years. Gender, educational level, and socioeconomic status were not statistically associated with suicidal ideation. Psychiatric disorders significantly associated with suicidal ideation were major depression (OR, 10.3; P < .001), panic disorder (OR, 5.2; P < .001), alcohol disorder (OR, 2.0; P = .04), and phobic disorder (OR, 1.6; P = .02) within the previous year. However, only 34% of respondents with suicidal ideation met criteria for major depression. With the aid of stepwise logistic regression, a four-item screening questionnaire, the Suicidal Ideation Screening Questionnaire, was developed to predict patients with suicidal ideation. Likelihood ratios for suicidal ideation increased from 0.21 to 32.8 with more positive responses to questions concerning symptoms of hopelessness, guilt, depressed mood, and sleep disturbances.
If the results from the four-item screen are reproduced in a clinical setting, general medical patients with a high likelihood for suicidal ideation may be identified with a brief screening questionnaire. This screen would have greater sensitivity than would be achieved by assessing suicidal ideation only in those patients who meet criteria for a distinct psychiatric disorder.
Bubbles excited by lithotripter shock waves undergo a prolonged growth followed by an inertial collapse and rebounds. In addition to the relevance for clinical lithotripsy treatments, such bubbles ...can be used to study the mechanics of inertial collapses. In particular, both phase change and diffusion among vapor and noncondensable gas molecules inside the bubble are known to alter the collapse dynamics of individual bubbles. Accordingly, the role of heat and mass transport during inertial collapses is explored by experimentally observing the collapses and rebounds of lithotripsy bubbles for water temperatures ranging from 20 to 60 °C and dissolved gas concentrations from 10 to 85% of saturation. Bubble responses were characterized through high-speed photography and acoustic measurements that identified the timing of individual bubble collapses. Maximum bubble diameters before and after collapse were estimated and the corresponding ratio of volumes was used to estimate the fraction of energy retained by the bubble through collapse. The rebounds demonstrated statistically significant dependencies on both dissolved gas concentration and temperature. In many observations, liquid jets indicating asymmetric bubble collapses were visible. Bubble rebounds were sensitive to these asymmetries primarily for water conditions corresponding to the most dissipative collapses.
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