From bottom to top The doubling of the number of transistors on a chip every 2 years, a seemly inevitable trend that has been called Moore's law, has contributed immensely to improvements in computer ...performance. However, silicon-based transistors cannot get much smaller than they are today, and other approaches should be explored to keep performance growing. Leiserson et al. review recent examples and argue that the most promising place to look is at the top of the computing stack, where improvements in software, algorithms, and hardware architecture can bring the much-needed boost. Science , this issue p. eaam9744
BACKGROUND Improvements in computing power can claim a large share of the credit for many of the things that we take for granted in our modern lives: cellphones that are more powerful than room-sized computers from 25 years ago, internet access for nearly half the world, and drug discoveries enabled by powerful supercomputers. Society has come to rely on computers whose performance increases exponentially over time. Much of the improvement in computer performance comes from decades of miniaturization of computer components, a trend that was foreseen by the Nobel Prize–winning physicist Richard Feynman in his 1959 address, “There’s Plenty of Room at the Bottom,” to the American Physical Society. In 1975, Intel founder Gordon Moore predicted the regularity of this miniaturization trend, now called Moore’s law, which, until recently, doubled the number of transistors on computer chips every 2 years. Unfortunately, semiconductor miniaturization is running out of steam as a viable way to grow computer performance—there isn’t much more room at the “Bottom.” If growth in computing power stalls, practically all industries will face challenges to their productivity. Nevertheless, opportunities for growth in computing performance will still be available, especially at the “Top” of the computing-technology stack: software, algorithms, and hardware architecture. ADVANCES Software can be made more efficient by performance engineering: restructuring software to make it run faster. Performance engineering can remove inefficiencies in programs, known as software bloat, arising from traditional software-development strategies that aim to minimize an application’s development time rather than the time it takes to run. Performance engineering can also tailor software to the hardware on which it runs, for example, to take advantage of parallel processors and vector units. Algorithms offer more-efficient ways to solve problems. Indeed, since the late 1970s, the time to solve the maximum-flow problem improved nearly as much from algorithmic advances as from hardware speedups. But progress on a given algorithmic problem occurs unevenly and sporadically and must ultimately face diminishing returns. As such, we see the biggest benefits coming from algorithms for new problem domains (e.g., machine learning) and from developing new theoretical machine models that better reflect emerging hardware. Hardware architectures can be streamlined—for instance, through processor simplification, where a complex processing core is replaced with a simpler core that requires fewer transistors. The freed-up transistor budget can then be redeployed in other ways—for example, by increasing the number of processor cores running in parallel, which can lead to large efficiency gains for problems that can exploit parallelism. Another form of streamlining is domain specialization, where hardware is customized for a particular application domain. This type of specialization jettisons processor functionality that is not needed for the domain. It can also allow more customization to the specific characteristics of the domain, for instance, by decreasing floating-point precision for machine-learning applications. In the post-Moore era, performance improvements from software, algorithms, and hardware architecture will increasingly require concurrent changes across other levels of the stack. These changes will be easier to implement, from engineering-management and economic points of view, if they occur within big system components: reusable software with typically more than a million lines of code or hardware of comparable complexity. When a single organization or company controls a big component, modularity can be more easily reengineered to obtain performance gains. Moreover, costs and benefits can be pooled so that important but costly changes in one part of the big component can be justified by benefits elsewhere in the same component. OUTLOOK As miniaturization wanes, the silicon-fabrication improvements at the Bottom will no longer provide the predictable, broad-based gains in computer performance that society has enjoyed for more than 50 years. Software performance engineering, development of algorithms, and hardware streamlining at the Top can continue to make computer applications faster in the post-Moore era. Unlike the historical gains at the Bottom, however, gains at the Top will be opportunistic, uneven, and sporadic. Moreover, they will be subject to diminishing returns as specific computations become better explored. Performance gains after Moore’s law ends. In the post-Moore era, improvements in computing power will increasingly come from technologies at the “Top” of the computing stack, not from those at the “Bottom”, reversing the historical trend. CREDIT: N. CARY/ SCIENCE
The miniaturization of semiconductor transistors has driven the growth in computer performance for more than 50 years. As miniaturization approaches its limits, bringing an end to Moore’s law, performance gains will need to come from software, algorithms, and hardware. We refer to these technologies as the “Top” of the computing stack to distinguish them from the traditional technologies at the “Bottom”: semiconductor physics and silicon-fabrication technology. In the post-Moore era, the Top will provide substantial performance gains, but these gains will be opportunistic, uneven, and sporadic, and they will suffer from the law of diminishing returns. Big system components offer a promising context for tackling the challenges of working at the Top.
A highly efficient thermal strategy to manage a high-powered Li-ion battery package within the required safe temperature range is of great demand for electric vehicles (EVs) applications. A ...sandwiched cooling structure using copper metal foam saturated with phase change materials was designed. The thermal efficiency of the system was experimentally evaluated and compared with two control cases: a cooling mode with pure phase change materials and an air-cooling mode. The results showed that the thermal management with air natural convection cannot fulfill the safety demand of the Li-ion battery. The use of pure PCM can dramatically reduce the surface temperature and maintain the temperature within an allowable range due to the latent heat absorption and the natural convection of the melted PCM during the melting process. The foam-paraffin composite further reduced the battery's surface temperature and improved the uniformity of the temperature distribution caused by the improvement of the effective thermal conductivity. Additionally, the battery surface temperature increased with an increase in the porosity and the pore density of the metal foam.
•Cooling structure for Li-ion battery using foam-paraffin composite was designed.•Thermal management by air natural convection cannot fulfill battery safety demand.•Employment of pure PCM dramatically reduced battery surface temperature.•Integration of copper foam and paraffin further reduced battery temperature.•Battery surface temperature increased with increase in porosity and pore density.
Different symmetry breaking ways determine various magnetization switching modes driven by spin-orbit torques (SOT). For instance, an applied or effective field parallel to applied current is ...indispensable to switch magnetization with perpendicular anisotropy by SOT. Besides of this mode, here we experimentally demonstrate a distinct field-free switching mode in a T-type magnetic system with structure of MgO/CoFeB/Ta/CoFeB/MgO where a perpendicular layer with tilted easy axis was coupled to an in-plane layer with a uniaxial easy axis. Current was applied orthogonal to both easy axes and thus also normal to an in-plane effective field experienced by the perpendicular layer. Dynamic calculation shows perpendicular layer could be switched at the same time as the in-plane layer is switched. These field-free switching modes realized in the same T-type magnetic system might expedite the birth of multi-state spin memories or spin logic devices which could be operated by all electric manners.
► A more detailed three-dimensional model of PTC was proposed by combining FVM and MCRT method. ► Corresponding codes and solving methods were developed and applied to an LS2 PTC. ► Numerical results ...proved that the model and method is feasible and reliable. ► More details of the characteristics in the receiver were revealed and discussed. ► Typical HTF types and residual gas conditions were further studied.
In this paper, a more detailed three-dimensional computational model of the whole parabolic trough solar collector (PTC) system and corresponding numerical simulations by combining the Finite Volume Method (FVM) and the Monte Carlo Ray-Trace (MCRT) method were presented. Corresponding codes and solving methods were also developed and applied to simulate and analyze the total involuted photo-thermal conversion process of an experimental LS2 PTC system. The numerical results were compared with experimental data and good agreement was obtained, proving that the model and method used in the present study is feasible and reliable. More details of the characteristics of solar concentrating, solar collecting, fluid dynamics, coupled heat transfer and the whole flow and temperature fields in the receiver were also revealed and discussed. Then some typical heat transfer fluid (HTF) types and residual gas conditions were further studied. It was revealed that the properties of these HTFs/conditions and their varying relations of the fluid temperature affected the characteristics of fluid dynamics, coupled heat transfer and the whole temperature distributions in the receiver, thus affected the thermal loss and the collector efficiency synthetically.
Objective The aim of this review was to systematically evaluate the associations of all-cause, cardiovascular and all-cancer mortality with primary ovarian insufficiency (POI) and early natural ...menopause (ENM).
Methods Electronic databases for relevant studies were searched up to February 28, 2015. POI and ENM were usually defined as spontaneous menopause before age 40 years and at age 40-44 years, respectively.
Results A total of nine articles were derived from seven prospective cohort studies. In all studies, age of menopause was self-reported. Our meta-analysis showed that POI women had a higher risk of death from all causes (pooled relative risk (RR) 1.39, 95% confidence interval (CI) 1.10-1.77) and ischemic heart disease (IHD) (pooled RR 1.48, 95% CI 1.02-2.16) when compared with women at normal age at natural menopause (ANM). No significant association was detected from stroke and all-cancer mortality between POI women and normal ANM women. Only a slightly higher risk of death from IHD (pooled RR 1.09, 95% CI 1.00-1.18) was found when ENM women were compared with normal ANM women.
Conclusion The results of our study demonstrated that POI was associated with a higher risk of IHD and all-cause mortality; ENM was only associated with a slightly higher risk of IHD mortality.
Some studies have found a significant relationship between birth weight (BW) and the risk of coronary heart disease (CHD) in adulthood, but results were inconsistent. The purpose of this study was to ...characterize the association between BW and the risk of CHD in adults. Among 144 papers detected by our search, 27 papers provided data on the relationship between BW and CHD, of which 23 papers considered BW as a continuous variable, and 14 articles considered BW as a categorical variable for this meta-analysis. Based on 23 papers, the mean weighted estimate for the association between BW and the combined outcome of non-fatal and fatal CHD was 0.83 95% confidence interval (CI), 0.80-0.86 per kilogram of BW (P<0.0001). Low birth weight (LBW<2500 g) was associated with increased risk of CHD odds ratio (OR), 1.19; 95% confidence interval (CI), 1.11-1.27 compared with subjects with BW⩾2500 g. LBW, as compared with normal BW (2500-4000 g), was associated with increased risk of CHD (OR, 1.16; 95% CI, 1.08-1.25). High birth weight (HBW⩾4000 g) was associated with decreased risk of CHD (OR, 0.89; 95% CI, 0.81-0.98) compared with subjects with BW<4000 g. In addition, there was an indication (not quite significant) that HBW was associated with a lower risk of CHD (OR, 0.89; 95% CI, 0.79-1.01), as compared with normal BW. No significant evidence of publication bias was present. These results suggest that LBW is significantly associated with increased risk of CHD and a 1 kg higher BW is associated with a 10-20% lower risk of CHD.
► Increasing HTF inlet parameters can improve PCTES performance. ► The inlet parameters restrict each other for the rated solar collector. ► The PCTES performance can be effectively enhanced by ...enhanced tubes. ► The pressure drops caused by the enhanced tubes could almost be neglected.
Based on enthalpy method, numerical studies were performed for high temperature molten salt phase change thermal energy storage (PCTES) unit used in a dish solar thermal power generation system. Firstly, the effects of the heat transfer fluid (HTF) inlet temperature and velocity on the PCTES performance were examined. The results show that although increasing the HTF inlet velocity or temperature can enhance the melting rate of the phase change material (PCM) and improve the performance of the PCTES unit, the two parameters will restrict each other for the fixed solar collector heat output. Then three enhanced tubes were adopted to improve the PCTES performance, which are dimpled tube, cone-finned tube and helically-finned tube respectively. The effects of the enhanced tubes on the PCM melting rate, solid–liquid interface, TES capacity, TES efficiency and HTF outlet temperature were discussed. The results show that compared with the smooth tube, all of the three enhanced tubes could improve the PCM melting rate. At the same working conditions, the melting time is 437.92min for the smooth tube, 350.75min for dimpled tube which is reduced about 19.9% and 320.25min for cone-finned tube which is reduced about 26.9% and 302.75min for helically-finned tube reduced about 30.7%. As a conclusion, the thermal performance of PCTES unit can be effectively enhanced by using enhanced tube instead of smooth tube. Although, the HTF pressure drops for the enhanced tubes are also larger than that of the smooth tube, the largest pressure drop (1476.2Pa) is still very lower compared with the working pressure (MPa magnitude) of the dish solar generation system. So, the pressure drops caused by the enhanced tubes could almost be neglected.
► Based on the unstable solar radiation, a model was established for phase change process under unsteady boundary. ► The PCM melting time decreases with the initial inlet temperature increase under ...the same average inlet temperature. ► The melting time reduces about 51.9% with the initial inlet temperature increase from 30°C to 90°C. ► The melting time decreases with the initial inlet mass flow rate increase under the same average inlet mass flow rate. ► The melting time reduces about 36.5% with the initial inlet mass flow rate increase from 2.0
×
10
−4
kg/s to 8.0
×
10
−4
kg/s.
Due to the solar radiation intensity variation over time, the outlet temperature or mass flow rate of heat transfer fluid (HTF) presents non-steady-state characteristics for solar collector. So, in the phase change thermal energy storage (PCTES) unit which is connected to solar collector, the phase change process occurs under the non-steady-state inlet boundary condition. In present paper, regarding the non-steady-state boundary, based on enthalpy method, a two dimensional physical and mathematical model for a shell-and-tube PCTES unit was established and the simulation code was self-developed. The effects of the non-steady-state inlet condition of HTF on the thermal performance of the PCTES unit were numerically analyzed. The results show that when the average HTF inlet temperature in an hour is fixed at a constant value, the melting time (time required for PCM completely melting) decreases with the increase of initial inlet temperature. When the initial inlet temperature increases from 30
°C to 90
°C, the melting time will decrease from 42.75
min to 20.58
min. However, the total TES capacity in an hour reduces from 338.9
kJ/kg to 211.5
kJ/kg. When the average inlet mass flow rate in an hour is fixed at a constant value, with the initial HTF inlet mass flow rate increasing, the melting time of PCM decreases. The initial inlet mass flow rate increasing from 2.0
×
10
−4
kg/s to 8.0
×
10
−4
kg/s will lead to the melting time decreasing from 37.42
min to 23.75
min and the TES capacity of PCM increasing from 265.8
kJ/kg to 273.8
kJ/kg. Under all the studied cases, the heat flux on the tube surface increases at first, until it reaches a maximum then it decreases over time. And the larger the initial inlet temperature or mass flow rate, the earlier the maximum value appearance and the larger the maximum value.
Introduction
Ketamine has been increasingly used to treat mental health conditions yet there is a lack of safety data on intramuscular (IM) and sublingual (SL) dosing in a community setting. The ...Roots to Thrive Ketamine assisted Therapy (RTT-KaT) program is a 12-week program with 12 Community of Practice (CoP) group therapy sessions and three ketamine sessions.
Objectives
To provide preliminary data on RTT-KAT adverse events to subsequently inform safe use of IM and SL ketamine for the treatment of psychiatric disorders.
Methods
Retrospective chart review of the RTT-KaT Program on four cohorts (n=128) between September 2020 to December 2021. Eligible patients include those with post-traumatic stress disorder, depression, generalized anxiety, burnout/adjustment disorder, substance use disorder, obsessive compulsive disorder, disordered eating, and disordered sleep. Baseline characteristics and adverse events were captured including medication administration before, during, and after RTT-KaT sessions. Chi-squared test with Yates’ continuity correction was used to assess side effects in subgroups from ketamine administration.
Results
RTT-KaT was well tolerated with no loss to follow up. There were 351 IM (mean dose = 102.553mg) and 96 SL (mean dose = 276.667mg) sessions of ketamine. Of the 448 sessions, the prevalence of elevated blood pressure increased by 12.31% from baseline (36.85%), with all post-treatment elevations being transient. The prevalence of elevated blood pressure post-KaT session was also similar between IM (+11.69% from 37.71% baseline) and SL (+15.12% from 32.98% baseline) administration. Regarding adverse effects, 12.05% of sessions experienced nausea , 2.52% had an episode of vomiting , 3.35% had a headache , and seven sessions experienced dizziness. The incidence of adverse events was not significantly associated with past psychedelic experiences (X2 = 0.0543, p-value = 0.8157), nor past psychiatric diagnosis (X2 = 0.0109, p-value = 0.917). . There was no significant association between administration route and incidence of nausea, which was the most common side effect(X2 = 1.112, p-value = 0.2916). Male gender was also significantly associated with lower incidence of nausea (X2 = 4.2841, p-value = 0.03847).
Conclusions
The group therapy model described provides a comprehensive approach and presents a promising model for operating a KaT program outside of a clinical trial setting.These findings suggest good safety and acceptability for RTT-KaT among individuals seeking treatment for mental health issues. Majority of participants did not experience adverse reactions and the adverse events that were recorded involved transient symptoms that were resolved with rest and/or medications.
Disclosure of Interest
None Declared
The solar energy flux distribution on the outer wall of the inner absorber tube of a parabolic solar collector receiver is calculated successfully by adopting the Monte Carlo Ray-Trace Method (MCRT ...Method). It is revealed that the non-uniformity of the solar energy flux distribution is very large. Three-dimensional numerical simulation of coupled heat transfer characteristics in the receiver tube is calculated and analyzed by combining the MCRT Method and the FLUENT software, in which the heat transfer fluid and physical model are Syltherm 800 liquid oil and LS2 parabolic solar collector from the testing experiment of Dudley et al., respectively. Temperature-dependent properties of the oil and thermal radiation between the inner absorber tube and the outer glass cover tube are also taken into account. Comparing with test results from three typical testing conditions, the average difference is within 2%. And then the mechanism of the coupled heat transfer in the receiver tube is further studied.
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