180 research outputs found

### Water productivity in agriculture: a review of empirical evidence for selected Asian countries and India

In the context of the growing demand for water and the emerging water crisis, this paper examines the prospects for improving water use efficiency in agriculture that will help water savings and also increase crop yields per unit of water input. Evidences from experimental or farmer participatory trials in a cross section of regions, countries, sites in Asia and the Indo-Gangetic plains suggest that alternate agronomic and crop management practices such as zero-tillage, bed planting, non-puddled rice culture and laser leveling can result in water savings and also improve rice and wheat yields per unit of water input.Length: pp.214-225Irrigation efficiencyWater productivityRiceWheat

### Efficiency at maximum power of minimally nonlinear irreversible heat engines

We propose the minimally nonlinear irreversible heat engine as a new general
theoretical model to study the efficiency at the maximum power $\eta^*$ of heat
engines operating between the hot heat reservoir at the temperature $T_h$ and
the cold one at $T_c$ ($T_c \le T_h$). Our model is based on the extended
Onsager relations with a new nonlinear term meaning the power dissipation. In
this model, we show that $\eta^*$ is bounded from the upper side by a function
of the Carnot efficiency $\eta_C\equiv 1-T_c/T_h$ as $\eta^*\le
\eta_C/(2-\eta_C)$. We demonstrate the validity of our theory by showing that
the low-dissipation Carnot engine can easily be described by our theory.Comment: 6 pages, 1 figur

### Molecular kinetic analysis of a finite-time Carnot cycle

We study the efficiency at the maximal power $\eta_\mathrm{max}$ of a
finite-time Carnot cycle of a weakly interacting gas which we can reagard as a
nearly ideal gas. In several systems interacting with the hot and cold
reservoirs of the temperatures $T_\mathrm{h}$ and $T_\mathrm{c}$, respectively,
it is known that $\eta_\mathrm{max}=1-\sqrt{T_\mathrm{c}/T_\mathrm{h}}$ which
is often called the Curzon-Ahlborn (CA) efficiency $\eta_\mathrm{CA}$. For the
first time numerical experiments to verify the validity of $\eta_\mathrm{CA}$
are performed by means of molecular dynamics simulations and reveal that our
$\eta_\mathrm{max}$ does not always agree with $\eta_\mathrm{CA}$, but
approaches $\eta_\mathrm{CA}$ in the limit of $T_\mathrm{c} \to T_\mathrm{h}$.
Our molecular kinetic analysis explains the above facts theoretically by using
only elementary arithmetic.Comment: 6 pages, 4 figure

### Onsager coefficients of a Brownian Carnot cycle

We study a Brownian Carnot cycle introduced by T. Schmiedl and U. Seifert
[Europhys. Lett. \textbf{81}, 20003 (2008)] from a viewpoint of the linear
irreversible thermodynamics. By considering the entropy production rate of this
cycle, we can determine thermodynamic forces and fluxes of the cycle and
calculate the Onsager coefficients for general protocols, that is, arbitrary
schedules to change the potential confining the Brownian particle. We show that
these Onsager coefficients contain the information of the protocol shape and
they satisfy the tight-coupling condition irrespective of whatever protocol
shape we choose. These properties may give an explanation why the
Curzon-Ahlborn efficiency often appears in the finite-time heat engines

### Coefficient of performance under optimized figure of merit in minimally nonlinear irreversible refrigerator

We apply the model of minimally nonlinear irreversible heat engines developed
by Izumida and Okuda [EPL {\bf 97}, 10004 (2012)] to refrigerators. The model
assumes extended Onsager relations including a new nonlinear term accounting
for dissipation effects. The bounds for the optimized regime under an
appropriate figure of merit and the tight-coupling condition are analyzed and
successfully compared with those obtained previously for low-dissipation Carnot
refrigerators in the finite-time thermodynamics framework. Besides, we study
the bounds for the nontight-coupling case numerically. We also introduce a
leaky low-dissipation Carnot refrigerator and show that it serves as an example
of the minimally nonlinear irreversible refrigerator, by calculating its
Onsager coefficients explicitly.Comment: Typo in eq.(34) is fixe

### Stochastic energetics of a Brownian motor and refrigerator driven by non-uniform temperature

The energetics of a Brownian heat engine and heat pump driven by position
dependent temperature, known as the B\"uttiker-Landauer heat engine and heat
pump, is investigated by numerical simulations of the inertial Langevin
equation. We identify parameter values for optimal performance of the heat
engine and heat pump. Our results qualitatively differ from approaches based on
the overdamped model. The behavior of the heat engine and heat pump, in the
linear response regime is examined under finite time conditions and we find
that the efficiency is lower than that of an endoreversible engine working
under the same condition. Finally, we investigate the role of different
potential and temperature profiles to enhance the efficiency of the system. Our
simulations show that optimizing the potential and temperature profile leads
only to a marginal enhancement of the system performance due to the large
entropy production via the Brownian particle's kinetic energy.Comment: 14 pages, 15 figures (latest version with modified figures and text

### Bounds of Efficiency at Maximum Power for Normal-, Sub- and Super-Dissipative Carnot-Like Heat Engines

The Carnot-like heat engines are classified into three types (normal-, sub-
and super-dissipative) according to relations between the minimum irreversible
entropy production in the "isothermal" processes and the time for completing
those processes. The efficiencies at maximum power of normal-, sub- and
super-dissipative Carnot-like heat engines are proved to be bounded between
$\eta_C/2$ and $\eta_C/(2-\eta_C)$, $\eta_C /2$ and $\eta_C$, 0 and
$\eta_C/(2-\eta_C)$, respectively. These bounds are also shared by linear, sub-
and super-linear irreversible Carnot-like engines [Tu and Wang, Europhys. Lett.
98, 40001 (2012)] although the dissipative engines and the irreversible ones
are inequivalent to each other.Comment: 1 figur

- …