Browsing by Subject "Cold Temperature"

Now showing 1 - 4 of 4
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    Dimensional study of the caging order parameter at the glass transition.
    (Proc Natl Acad Sci U S A, 2012-08-28) Charbonneau, Patrick; Ikeda, Atsushi; Parisi, Giorgio; Zamponi, Francesco
    The glass problem is notoriously hard and controversial. Even at the mean-field level, little is agreed upon regarding why a fluid becomes sluggish while exhibiting but unremarkable structural changes. It is clear, however, that the process involves self-caging, which provides an order parameter for the transition. It is also broadly assumed that this cage should have a gaussian shape in the mean-field limit. Here we show that this ansatz does not hold. By performing simulations as a function of spatial dimension d, we find the cage to keep a nontrivial form. Quantitative mean-field descriptions of the glass transition, such as mode-coupling theory, density functional theory, and replica theory, all miss this crucial element. Although the mean-field random first-order transition scenario of the glass transition is qualitatively supported here and non-mean-field corrections are found to remain small on decreasing d, reconsideration of its implementation is needed for it to result in a coherent description of experimental observations.
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    Estimating the effects of vegetation and increased albedo on the urban heat island effect with spatial causal inference.
    (Scientific reports, 2024-01) Calhoun, Zachary D; Willard, Frank; Ge, Chenhao; Rodriguez, Claudia; Bergin, Mike; Carlson, David
    The urban heat island effect causes increased heat stress in urban areas. Cool roofs and urban greening have been promoted as mitigation strategies to reduce this effect. However, evaluating their efficacy remains a challenge, as potential temperature reductions depend on local characteristics. Existing methods to characterize their efficacy, such as computational fluid dynamics and urban canopy models, are computationally burdensome and require a high degree of expertise to employ. We propose a data-driven approach to overcome these hurdles, inspired by recent innovations in spatial causal inference. This approach allows for estimates of hypothetical interventions to reduce the urban heat island effect. We demonstrate this approach by modeling evening temperature in Durham, North Carolina, using readily retrieved air temperature, land cover, and satellite data. Hypothetical interventions such as lining streets with trees, cool roofs, and changing parking lots to green space are estimated to decrease evening temperatures by a maximum of 0.7-0.9   [Formula: see text], with reduced effects on temperature as a function of distance from the intervention. Because of the ease of data access, this approach may be applied to other cities in the U.S. to help them come up with city-specific solutions for reducing urban heat stress.
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    Prolactin receptor signaling is essential for perinatal brown adipocyte function: a role for insulin-like growth factor-2.
    (PLoS One, 2008-02-06) Viengchareun, Say; Servel, Nathalie; Fève, Bruno; Freemark, Michael; Lombès, Marc; Binart, Nadine
    BACKGROUND: The lactogenic hormones prolactin (PRL) and placental lactogens (PL) play central roles in reproduction and mammary development. Their actions are mediated via binding to PRL receptor (PRLR), highly expressed in brown adipose tissue (BAT), yet their impact on adipocyte function and metabolism remains unclear. METHODOLOGY/PRINCIPAL FINDINGS: PRLR knockout (KO) newborn mice were phenotypically characterized in terms of thermoregulation and their BAT differentiation assayed for gene expression studies. Derived brown preadipocyte cell lines were established to evaluate the molecular mechanisms involved in PRL signaling on BAT function. Here, we report that newborn mice lacking PRLR have hypotrophic BAT depots that express low levels of adipocyte nuclear receptor PPARgamma2, its coactivator PGC-1alpha, uncoupling protein 1 (UCP1) and the beta3 adrenoceptor, reducing mouse viability during cold challenge. Immortalized PRLR KO preadipocytes fail to undergo differentiation into mature adipocytes, a defect reversed by reintroduction of PRLR. That the effects of the lactogens in BAT are at least partly mediated by Insulin-like Growth Factor-2 (IGF-2) is supported by: i) a striking reduction in BAT IGF-2 expression in PRLR KO mice and in PRLR-deficient preadipocytes; ii) induction of cellular IGF-2 expression by PRL through JAK2/STAT5 pathway activation; and iii) reversal of defective differentiation in PRLR KO cells by exogenous IGF-2. CONCLUSIONS: Our findings demonstrate that the lactogens act in concert with IGF-2 to control brown adipocyte differentiation and growth. Given the prominent role of brown adipose tissue during the perinatal period, our results identified prolactin receptor signaling as a major player and a potential therapeutic target in protecting newborn mammals against hypothermia.
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    Swimming-Induced Pulmonary Edema: Pathophysiology and Risk Reduction With Sildenafil.
    (Circulation, 2016-03-08) Moon, RE; Peacher, DF; Potter, JF; Wester, TE; Cherry, AD; Natoli, M; Otteni, CE; Kernagis, DN; White, WD; Freiberger, J
    BACKGROUND: Swimming-induced pulmonary edema (SIPE) occurs during swimming or scuba diving, often in young individuals with no predisposing conditions, and its pathophysiology is poorly understood. This study tested the hypothesis that pulmonary artery and pulmonary artery wedge pressures are higher in SIPE-susceptible individuals during submerged exercise than in the general population and are reduced by sildenafil. METHODS AND RESULTS: Ten study subjects with a history of SIPE (mean age, 41.6 years) and 20 control subjects (mean age, 36.2 years) were instrumented with radial artery and pulmonary artery catheters and performed moderate cycle ergometer exercise for 6 to 7 minutes while submersed in 20°C water. SIPE-susceptible subjects repeated the exercise 150 minutes after oral administration of 50 mg sildenafil. Work rate and mean arterial pressure during exercise were similar in controls and SIPE-susceptible subjects. Average o2 and cardiac output in controls and SIPE-susceptible subjects were: o2 2.42 L·min(-1) versus 1.95 L·min(-1), P=0.2; and cardiac output 17.9 L·min(-1) versus 13.8 L·min(-1), P=0.01. Accounting for differences in cardiac output between groups, mean pulmonary artery pressure at cardiac output=13.8 L·min(-1) was 22.5 mm Hg in controls versus 34.0 mm Hg in SIPE-susceptible subjects (P=0.004), and the corresponding pulmonary artery wedge pressure was 11.0 mm Hg versus 18.8 mm Hg (P=0.028). After sildenafil, there were no statistically significant differences in mean pulmonary artery pressure or pulmonary artery wedge pressure between SIPE-susceptible subjects and controls. CONCLUSIONS: These observations confirm that SIPE is a form of hemodynamic pulmonary edema. The reduction in pulmonary vascular pressures after sildenafil with no adverse effect on exercise hemodynamics suggests that it may be useful in SIPE prevention. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00815646.