The recent success of continuous-flow circulatory support devices has led to the growing acceptance of these devices as a viable therapeutic option for end-stage heart failure patients who are not ...responsive to current pharmacologic and electrophysiologic therapies. This article defines and clarifies the major classification of these pumps as axial or centrifugal continuous-flow devices by discussing the difference in their inherent mechanics and describing how these features translate clinically to pump selection and patient management issues. Axial vs centrifugal pump and bearing design, theory of operation, hydrodynamic performance, and current vs flow relationships are discussed. A review of axial vs centrifugal physiology, pre-load and after-load sensitivity, flow pulsatility, and issues related to automatic physiologic control and suction prevention algorithms is offered. Reliability and biocompatibility of the two types of pumps are reviewed from the perspectives of mechanical wear, implant life, hemolysis, and pump deposition. Finally, a glimpse into the future of continuous-flow technologies is presented.
Parity-time–symmetric microring lasers Hodaei, Hossein; Miri, Mohammad-Ali; Heinrich, Matthias ...
Science (American Association for the Advancement of Science),
11/2014, Letnik:
346, Številka:
6212
Journal Article
Recenzirano
The ability to control the modes oscillating within a laser resonator is of fundamental importance. In general, the presence of competing modes can be detrimental to beam quality and spectral purity, ...thus leading to spatial as well as temporal fluctuations in the emitted radiation. We show that by harnessing notions from parity-time (PT) symmetry, stable single–longitudinal mode operation can be readily achieved in a system of coupled microring lasers. The selective breaking of PT symmetry can be used to systematically enhance the maximum attainable output power in the desired mode. This versatile concept is inherently self-adapting and facilitates mode selectivity over a broad bandwidth without the need for other additional intricate components. Our experimental findings provide the possibility to develop synthetic optical devices and structures with enhanced functionality.
Summary
MIL‐100(Fe) with good hydrothermal stability and high hydrophilicity is considered to be a potential adsorbent for adsorption heat pumps (AHPs). However, its water vapor adsorption ...performance at low relative humidity needs to be improved. In this study, composite adsorbent LiCl@MIL‐100(Fe) was synthesized by impregnating LiCl aqueous solution in MIL‐100(Fe). The effects of the LiCl loading in the composite on the crystal structure, morphology, composition, pore structure as well as the vapor adsorption/desorption performance of the composites were carefully studied. The results showed that on the premise of ensuring no leakage, the LiCl loading in the composite was up to 32.9 wt%. At 20% relative humidity (RH), the saturated adsorption ratio of the composite (0.260 g/g) was higher than that of original MIL‐100(Fe) (0.054 g/g). Meanwhile, the water adsorption rate of the new composite adsorbent was faster than pristine MIL‐100(Fe). Moreover, after 50 cycles of vapor adsorption/desorption, the composite adsorbent showed a satisfactory stability. All these indicate that the new LiCl@MIL‐100(Fe) composite adsorbent will be a prospective candidate for high‐efficiency AHPs.
•Experimental data of frost formation on a microchannel heat exchanger.•Impacts of relative humidity, face velocity, and fouling level.•Surprisingly, light fouling increased heat transfer 1% and ...frost formation rate 19%.•Heavy fouling decreased the heat transfer and frost formation rates.
Air source heat pumps have the potential to efficiently heat and cool buildings, but their effectiveness in many climates is limited by frost growth on the outdoor heat exchanger in heating mode. These heat exchanger coils are also subject to fouling from fibers and particulates outdoors. Frost and fouling have each independently been studied extensively, and newly available research on fouling provides a method to realistically foul the air-side of coils in the laboratory. The current paper uses this method to conduct the first laboratory study of the important interactions between fouling and frost growth for a heat pump outdoor coil. A microchannel heat exchanger is tested clean and fouled, with variations in fouling level, humidity, and initial face velocity of air. Air flow rate is allowed to vary with resistance, and a surprising result is that light fouling increases heat transfer and frost growth rates, even with a 3.5% reduction in initial airflow caused by the fouling. However, heavier fouling decreases both rates. When frost growth is normalized to heat transfer, it is found to be increased by fouling; i.e. the coil's sensible heat ratio decreases.
•A load-based testing and performance rating approach for residential cooling equipment is developed.•Test equipment with its native controls behaves as if it were installed in the field.•Test is ...automated by implementing standardized procedures and convergence criteria.•Climate-specific seasonal performance ratings are generated from test results.•The proposed approach was implemented to a variable-speed heat pump.
In the U.S., with about 64% of primary occupied homes having unitary air conditioners, a small improvement in the energy efficiency of residential cooling equipment can lead to significant energy savings. Currently, standardized equipment energy efficiency rating is based on standard AHRI 210/240, that provides a metric for comparing the performance of different equipment. However, it is generally recognized that this approach fails to appropriately rate and credit equipment with advanced controls and variable-speed components. Contrarily, a load-based testing and rating approach is presented in this paper that can capture equipment performance with its integrated controls that is more representative of the field. In this approach, representative building sensible and latent loads are emulated in a psychrometric test facility at different indoor and outdoor test conditions utilizing a virtual building model. The indoor test room conditions are continuously adjusted to emulate the dynamic response of the virtual building to the test equipment sensible and latent cooling rates and the equipment dynamic response is measured. Moreover, an automated testing procedure is presented along with convergence criteria for measuring equipment steady-periodic performance. Climate-specific cooling seasonal performance ratings can be determined by propagating the coefficient of performance (COP) from load-based testing results through a temperature-bin method to estimate a seasonal COP (SCOP). In this work, the proposed approach was implemented to test and rate a variable-speed residential heat pump. Furthermore, the sensitivity of load-based testing results to virtual building parameters was investigated. Finally, repeatability results from the load-based testing approach are presented.
We describe generation of stable mode-locked pulse trains from on-chip normal dispersion microresonators. The excitation of hyperparametric oscillation is facilitated by the local dispersion ...disruptions induced by mode interactions. The system is then driven from hyperparametric oscillation to the mode-locked state with over 200 nm spectral width by controlled pump power and detuning. With the continuous-wave-driven nonlinearity, the pulses sit on a pedestal, akin to a cavity soliton. We identify the importance of pump detuning and wavelength-dependent quality factors in stabilizing and shaping the pulse structure, to achieve a single pulse inside the cavity. We examine the mode-locking dynamics by numerically solving the master equation and provide analytic solutions under appropriate approximations.
Sudden unexpected death in infancy occurs in apparently healthy infants and remains largely unexplained despite thorough investigation. The vast majority of cases are sporadic. Here we report seven ...individuals from three families affected by sudden and unexpected cardiac arrest between 4 and 20 months of age. Whole-exome sequencing revealed compound heterozygous missense mutations in PPA2 in affected infants of each family. PPA2 encodes the mitochondrial pyrophosphatase, which hydrolyzes inorganic pyrophosphate into two phosphates. This is an essential activity for many biosynthetic reactions and for energy metabolism of the cell. We show that deletion of the orthologous gene in yeast (ppa2Δ) compromises cell viability due to the loss of mitochondria. Expression of wild-type human PPA2, but not PPA2 containing the mutations identified in affected individuals, preserves mitochondrial function in ppa2Δ yeast. Using a regulatable (doxycycline-repressible) gene expression system, we found that the pathogenic PPA2 mutations rapidly inactivate the mitochondrial energy transducing system and prevent the maintenance of a sufficient electrical potential across the inner membrane, which explains the subsequent disappearance of mitochondria from the mutant yeast cells. Altogether these data demonstrate that PPA2 is an essential gene in yeast and that biallelic mutations in PPA2 cause a mitochondrial disease leading to sudden cardiac arrest in infants.
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•Relative humidity has a performance enhancing effect above frosting conditions.•The effect of relative humidity on performance is after a limit value.•Outdoor temperature rise highly ...improves performance.•Higher capacity air conditioners performs better performance in colder climates.•Deriving the COP change rate correlation with temperature and relative humidity.
The paper investigates the performance effect of outdoor temperature and relative humidity on ASHP performance above frosting conditions, with the developed mathematical model. The model results are validated with the experimental data available in literature, of four ASHPs in the 2.7 kW−5.8 kW capacity range. 4 kW capacity ASHP is taken as reference. Constant heating (CH), constant work (CW) and variable heating (VH) modes are determined as operating modes. The model results reveal that relative humidity is a performance enhancing factor above frosting conditions. In VH mode, which is the most realistic operating mode for residences, raise in outdoor temperature from 7 °C to 14 °C increases the COP value by 30%, and raise in the relative humidity from 0.6 to 1.0 provides an additional 5% COP increase. In CH and CW modes, the contribution of relative humidity to performance increases with temperature, up to 10.7% and 6.4%, respectively. Correlations giving the COP change rate with respect to ambient temperature and relative humidity are derived with higher than 0.9839 R2 values for dry and humid conditions of the CH, CW and VH operating modes. These correlations can be useful for researchers who intends to analyze ASHP performance based on ambient conditions.
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