Hasil untuk "Heat"

Nianbei Li, Jie Ren, Lei Wang et al.

The form of energy termed heat that typically derives from lattice vibrations, i.e., phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, in this Colloquium, an attempt is made to rebut this common view: By use of tailored models it is demonstrated that phonons can be manipulated similarly to electrons and photons, thus enabling controlled heat transport. Moreover, it is explained that phonons can be put to beneficial use to carry and process information. In the first part ways are presented to control heat transport and to process information for physical systems which are driven by a temperature bias. In particular, a toolkit of familiar electronic analogs for use of phononics is put forward, i.e., phononic devices are described which act as thermal diodes, thermal transistors, thermal logic gates, and thermal memories. These concepts are then put to work to transport, control, and rectify heat in physically realistic nanosystems by devising practical designs of hybrid nanostructures that permit the operation of functional phononic devices; the first experimental realizations are also reported. Next, richer possibilities to manipulate heat flow by use of time-varying thermal bath temperatures or various other external fields are discussed. These give rise to many intriguing phononic nonequilibrium phenomena such as, for example, the directed shuttling of heat, geometrical phase-induced heat pumping, or the phonon Hall effect, which may all find their way into operation with electronic analogs.

G. Anderson, Michelle L. Bell

Background Devastating health effects from recent heat waves, and projected increases in frequency, duration, and severity of heat waves from climate change, highlight the importance of understanding health consequences of heat waves. Objectives We analyzed mortality risk for heat waves in 43 U.S. cities (1987–2005) and investigated how effects relate to heat waves’ intensity, duration, or timing in season. Methods Heat waves were defined as ≥ 2 days with temperature ≥ 95th percentile for the community for 1 May through 30 September. Heat waves were characterized by their intensity, duration, and timing in season. Within each community, we estimated mortality risk during each heat wave compared with non-heat wave days, controlling for potential confounders. We combined individual heat wave effect estimates using Bayesian hierarchical modeling to generate overall effects at the community, regional, and national levels. We estimated how heat wave mortality effects were modified by heat wave characteristics (intensity, duration, timing in season). Results Nationally, mortality increased 3.74% [95% posterior interval (PI), 2.29–5.22%] during heat waves compared with non-heat wave days. Heat wave mortality risk increased 2.49% for every 1°F increase in heat wave intensity and 0.38% for every 1-day increase in heat wave duration. Mortality increased 5.04% (95% PI, 3.06–7.06%) during the first heat wave of the summer versus 2.65% (95% PI, 1.14–4.18%) during later heat waves, compared with non-heat wave days. Heat wave mortality impacts and effect modification by heat wave characteristics were more pronounced in the Northeast and Midwest compared with the South. Conclusions We found higher mortality risk from heat waves that were more intense or longer, or those occurring earlier in summer. These findings have implications for decision makers and researchers estimating health effects from climate change.

M. Farooq, H. Bramley, J. Palta et al.

G. Luber, M. Mcgeehin

M. Kryder, E. Gage, T. McDaniel et al.

M. Araújo, F. Ferri‐Yáñez, F. Bozinovic et al.

Climate change is altering phenology and distributions of many species and further changes are projected. Can species physiologically adapt to climate warming? We analyse thermal tolerances of a large number of terrestrial ectotherm (n = 697), endotherm (n = 227) and plant (n = 1816) species worldwide, and show that tolerance to heat is largely conserved across lineages, while tolerance to cold varies between and within species. This pattern, previously documented for ectotherms, is apparent for this group and for endotherms and plants, challenging the longstanding view that physiological tolerances of species change continuously across climatic gradients. An alternative view is proposed in which the thermal component of climatic niches would overlap across species more than expected. We argue that hard physiological boundaries exist that constrain evolution of tolerances of terrestrial organisms to high temperatures. In contrast, evolution of tolerances to cold should be more frequent. One consequence of conservatism of upper thermal tolerances is that estimated niches for cold-adapted species will tend to underestimate their upper thermal limits, thereby potentially inflating assessments of risk from climate change. In contrast, species whose climatic preferences are close to their upper thermal limits will unlikely evolve physiological tolerances to increased heat, thereby being predictably more affected by warming.

A. Bejan

L. Baumgard, R. Rhoads

J. Hendrick, F. Hartl

E. N. Sieder, G. E. Tate

Carl Wu

F. Kreith, M. Bohn, A. Kirkpatrick

R. Morimoto

J. Zou, Yongle Guo, T. Guettouche et al.

E. Eckert, R. Drake

I. Sȃrbu, Călin Sebarchievici

M. Sheikholeslami, M. Gorji-Bandpy, D. Ganji

K. Barlow, B. Christy, G. O'Leary et al.

Abstract Extreme weather events (frost and heat shock), already a significant challenge for grain producers, are predicted to increase under future climate scenarios. This paper reviews the current knowledge on the impacts of extreme heat (heat shock) and frost on crop production and how these impacts are incorporated into contemporary process-based crop models. Heat shock and frost result in a range of physiological impacts on wheat. Based on the literature we conclude that the greatest impacts on production from frost are associated with sterility and the abortion of formed grains around anthesis. While the greatest yield impact from heat shock are reduced grain number (sterility and abortion of grains) during anthesis to early grain filling; as well as the reduced duration of grain filling. Crop models generally did not consider the non-linear response in grain yield from a heat shock or frost event due to these key physiological impacts. While frost damage was incorporated into a number of models through winterkill functions, seedling death or advanced senescence, only the STICS model incorporated a potential decrease in grain number around anthesis. In contrast, heat shock was rarely considered within crop models, with only two examples found in the literature; (1) APSIM-Nwheat which incorporated accelerated senescence in response to extreme heat and (2) MONICA which incorporated a reduction in grain number and yield. We propose a conceptual model for the change in grain number and therefore yield in response to both a frost and heat shock event. We discuss the potential use of daily maximum/minimum temperatures, canopy temperature and heat/frost loads for determining crop response in the models. As well as identifying the need for a greater understanding on how the duration of temperature extremes impact on yield, as well as the cumulative effects of multiple heat/frost events and the interactions with other abiotic stresses including drought.

M. Rathod, J. Banerjee

Neil Debbage, J. M. Shepherd