6,288 research outputs found
Recommended from our members
Delayed chilling appears to counteract flowering advances of apricot in southern UK
Temperatures are rising across the globe, and the UK is no
exception. Spring phenology of perennial fruit crops is to a large extent
determined by temperature during effective chilling (endo-dormancy) and
heat accumulation (eco-dormancy) periods. We used the apricot flowering
records of the UK National Fruit Collections (NFC) to determine the
influence of temperature trends over recent decades (1960 to 2014) on
apricot (Prunus armeniaca L.) flowering time. Using Partial Least Squares
(PLS) regression, we determined the respective periods for calculating
chill and heat accumulation. Results suggested intervals between
September 27th and February 26th and between December 31st and April 12th
as the effective chilling and warming periods, respectively. Flowering
time was correlated with temperature during both periods, with warming
during chilling corresponding to flowering delays by 4.82 d°C-1, while
warming during heat accumulation was associated with bloom advances by
9.85 d°C-1. Heat accumulation started after accumulating 62.7 ± 5.6 Chill
Portions, and flowering occurred after a further 3744 ± 1538 Growing
Degree Hours (above a base temperature of 4°C, with optimal growth at
26°C). When examining the time series, the increase in temperature during
the chilling period did not appear to decrease overall chill accumulation
during the chilling period but to delay the onset of chill accumulation
and the completion of the the average chill accumulation necessary to
start heat accumulation. The resulting delay in heat responsiveness
appeared to weaken the phenology-advancing effect of spring warming.
These processes may explain why apricot flowering time remained
relatively unchanged despite significant temperature increases. A
consequence of this may be a reduction of frost risk for early flowering
crops such as apricot in the UK
Spin heat accumulation and its relaxation in spin valves
We study the concept of spin heat accumulation in excited spin valves, more
precisely the effective electron temperature that may become spin dependent,
both in linear response and far from equilibrium. A temperature or voltage
gradient create non-equilibrium energy distributions of the two spin ensembles
in the normal metal spacer, which approach Fermi-Dirac functions through energy
relaxation mediated by electron-electron and electron-phonon coupling. Both
mechanisms also exchange energy between the spin subsystems. This inter-spin
energy exchange may strongly affect thermoelectric properties spin valves,
leading, e.g., to violations of the Wiedemann-Franz law.Comment: 4 pages, 4 figures, close to published versio
Recommended from our members
High repetition rate femtosecond laser heat accumulation and ablation thresholds in cobalt-binder and binderless tungsten carbides
Femtosecond (fs) laser ablation has been studied for the potential of fast, high precision machining of difficult-to-machine materials like binderless tungsten carbide. Obstacles that have limited its efficiency include melting from heat accumulation (HA), particle shielding, and plasma shielding. To address HA without shielding effects, high repetition rate (57.4 MHz), ultra-low fluence fs laser irradiation is performed to study the incubation effect and subsequent HA-ablation threshold of fine-grained tungsten carbides. Exposure times on the order of 100 ms were conducted in air with fluences (1.82 to 9.09 mJ/cm2) two orders of magnitude below the single fs pulse ablation thresholds reported in literature (0.4 J/cm2). Heat accumulation at high repetition rate explains the ultra-low fluence melt threshold behavior resulting in melt crowns around ablated holes and grooves. The results of this study aid in predicting heat buildup in high repetition rate laser irradiation for applications that wish to achieve high ablation rates of difficult-to-machine, ultrahard materials and help enable shaping of binderless tungsten carbide for use in applications too extreme for bindered tungsten carbide
Thermal Spin-Transfer Torques in Magnetoelectronic Devices
We predict that the magnetization direction of a ferromagnet can be reversed
by the spin-transfer torque accompanying spin-polarized thermoelectric heat
currents. We illustrate the concept by applying a finite-element theory of
thermoelectric transport in disordered magnetoelectronic circuits and devices
to metallic spin valves. When thermalization is not complete, a spin heat
accumulation vector is found in the normal metal spacer, i.e., a directional
imbalance in the temperature of majority and minority spins.Comment: Accepted for publication by Physical Review Letter
Meshless Simulation of Multi-site Radio Frequency Catheter Ablation through the Fragile Points Method
Computational models for radio frequency
catheter ablation (RFCA) of cardiac arrhythmia have been
developed and tested in conditions where a single ablation
site is considered. However, in reality arrhythmic events
are generated at multiple sites which are ablated during
treatment. Under such conditions, heat accumulation from
several ablations is expected and models should take this effect
into account. Moreover, such models are solved using the
Finite Element Method which requires a good quality mesh
to ensure numerical accuracy. Therefore, clinical application
is limited since heat accumulation effects are neglected and
numerical accuracy depends on mesh quality. In this work, we
propose a novel meshless computational model where tissue
heat accumulation from previously ablated sites is taken into
account. In this way, we aim to overcome the mesh quality
restriction of the Finite Element Method and enable realistic
multi-site ablation simulation. We consider a two ablation
sites protocol where tissue temperature at the end of the first
ablation is used as initial condition for the second ablation. The
effect of the time interval between the ablation of the two sites
is evaluated. The proposed method demonstrates that previous
models that do not account for heat accumulation between
ablations may underestimate the tissue heat distribution
Dynamic Behavior of Reverse Flow Reactor for Lean Methane Combustion
The stability of reactor operation for catalytic oxidation of lean CH4 has been investigated through modeling and simulation, particularly the influence of switching time and heat extraction on reverse flow reactor (RFR) performance. A mathematical model of the RFR was developed, based on one-dimensional pseudo-homogeneous model for mass and heat balances, incorporating heat loss through the reactor wall. The configuration of the RFR consisted of inert-catalyst-inert, with or without heat extraction that makes it possible to store the energy released by the exothermic reaction of CH4 oxidation. The objective of this study was to investigate the dynamic behavior of the RFR for lean methane oxidation and to find the optimum condition by exploring a stability analysis of the simple reactor. The optimum criteria were defined in terms of CH4 conversion, CH4 slip, and heat accumulation in the RFR. At a switching time of 100 s, the CH4 conversion reached the maximum value, while the CH4 slip attained its minimum value. The RFR could operate autothermally with positive heat accumulation, i.e. 0.02 J/s. The stability of the RFR in terms of heat accumulation was achieved at a switching time of 100 s
Applying the USA National Phenology Network\u27s Growing Degree Day Maps in Making Management Decisions
The USA National Phenology Network generates daily growing degree day maps for the United States at fine spatial resolution (2.5–3.0 km) using a January 1 start date and two common base temperatures. Maps are available up to 6 days into the future and can be viewed and manipulated using an online visualization tool or downloaded as image or raster files. By exploring these maps through the visualization tool, it is possible to see how heat accumulation over the course of the year varies from average conditions and to anticipate when heat accumulation thresholds will be met
The gravitational heat conduction and the hierarchical structure in solar interior
With the assumption of local Tsallis equilibrium, the newly defined
gravitational temperature is calculated in the solar interior, whose
distribution curve can be divided into three parts, the solar core region,
radiation region and convection region, in excellent agreement with the solar
hierarchical structure. By generalizing the Fourier law, one new mechanism of
heat conduction, based on the gradient of the gravitational temperature, is
introduced into the astrophysical system. This mechanism is related to the
self-gravity of such self-gravitating system whose characteristic scale is
large enough. It perhaps plays an important role in the astrophysical system
which, in the solar interior, leads to the heat accumulation at the bottom of
the convection layer and then motivates the convection motion.Comment: 8 pages, 2 figures, 1 table, 19 reference
- …