Thermal Modeling of Metal Powder-Based Selective Laser Sintering

In order to get a better understanding of Selective Laser Sintering (SLS) process of the metal powders, three-dimensional modeling of laser sintering of a metal powder mixture that contains two kinds of metal powder with significantly different melting points under a moving Gaussian laser beam is investigated numerically. Laser induced melting and resolidification accompanied by shrinkage are modeled using a temperature transforming model. The liquid flow of the melted low melting point metal driven by capillary and gravity forces is also included in the physical model. Both complete and partial shrinkages are considered in the model. Simulations are performed for both single line laser scanning and multiple-line laser scanning. The numerical results are compared with experimental results and a detailed parametric study is performed. The effects of the moving heat source intensity, the scanning velocity, the thickness of the powder layer and the number of existing sintered layers underneath on the sintering depth, the shape of the heat affected zone (HAZ) and the temperature distribution are discussed. The optimized dimensionless moving heat source intensity increases with increasing scanning velocity in order to achieve the desired sintering depth and bond the newly sintered layer to the previously sintered layers.Mechanical Engineerin

Two-Dimensional Modeling of Sintering of a Two-Component Metal Powder Layer on Top of Multiple Sintered Layers with a Moving Gaussian Heat Source

Selective Laser Sintering (SLS) of metal powder is modeled as a two-dimensional melting and resolidification of a loose powder layer on top of the sintered metal layers with a moving heat source. The shrinkage induced by melting is accounted for and the problem is modeled using a temperature-transforming model. The results indicate that both the moving heat source intensity and scanning velocity have significant effects on the sintering process. Since the thermal conductivity of the sintered layer is relatively high compared with that of the loose powder, higher heat source intensity and lower scanning velocity are needed to achieve complete melting of the loose powder and bond the current layer to the existing sintered layers. A parametric study is performed and the best combinations of the processing parameters are recommended.Support for this work by the Office of Naval Research under grant number N00014-02-1- 0356 is greatly acknowledged.Mechanical Engineerin

Meta-analysis of Incidence of Brain Cancer Among Aircrew

Introduction: Previous studies on Brain and other Nervous System Cancers (BNSC) and aircrew have shown inconsistent results, possibly due to their relatively small sample sizes; therefore, the current study aimed to increase the precision of risk estimates.Methods: Systematic searches of PubMed and Embase for pertinent studies up to August 2016 were performed and supplemented by manual reviews of bibliographies. The pooled standard incidence ratio (SIR) and corresponding 95% CIs were estimated with random effects models.Results: Among the 903 studies retrieved, 7 studies (5 cohort studies and 2 pooled analyses) were included in the current meta-analysis. The pooled SIR (95% CI) of BNSC incidence in aircrew was 1.01 (0.77, 1.31) with no significant heterogeneity (I2 = 36.1%, P = .199). The null association persisted when the analysis was stratified by geographic area (Europe or America), publication year (before or after 2001), air population (pilots or cabin crew), cancer site (brain, nervous system, or brain/nervous system), and gender (male or female).Conclusion: The current evidence is not sufficient to support a significant positive association between aircrew employment and BNSC risk. However, the interpretation and extrapolation of this meta-analysis are restricted by the possible impact exerted by health worker effect and potential clinical heterogeneity. More studies based on other populations, including Asian aircrews, are warranted

Npy deletion in an alcohol non-preferring rat model elicits differential effects on alcohol consumption and body weight.

Neuropeptide Y (NPY) is widely expressed in the central nervous system and influences many physiological processes. It is located within the rat quantitative trait locus (QTL) for alcohol preference on chromosome 4. Alcohol-nonpreferring (NP) rats consume very little alcohol, but have significantly higher NPY expression in the brain than alcohol-preferring (P) rats. We capitalized on this phenotypic difference by creating an Npy knockout (KO) rat using the inbred NP background to evaluate NPY effects on alcohol consumption. Zinc finger nuclease (ZNF) technology was applied, resulting in

The Performance and Energy Consumption of Embedded Real-Time Operating Systems

This paper presents the modeling of embedded systems with SimBed, an execution-driven simulation testbed that measures the execution behavior and power consumption of embedded applications and RTOSs by executing them on an accurate architectural model of a microcontroller with simulated real-time stimuli. We briefly describe the simulation environment and present a study that compares three RTOSs: μ C/OS-II, a popular public-domain embedded real-time operating system; Echidna, a sophisticated, industrial-strength (commercial) RTOS; and NOS, a bare-bones multi-rate task scheduler reminiscent of typical “roll-your-own” RTOSs found in many commercial embedded systems. The microcontroller simulated in this study is the Motorola M-CORE processor: a low-power, 32-bit CPU core with 16-bit instructions, running at 20MHz. Our simulations show what happens when RTOSs are pushed beyond their limits, and they depict situations in which unexpected interrupts or unaccounted-for task invocations disrupt timing, even when the CPU is lightly loaded. In general, there appears no clear winner in timing accuracy between preemptive systems and cooperative systems. The power-consumption measurements show that RTOS overhead is a factor of two to four higher than it needs to be, compared to the energy consumption of the minimal scheduler. In addition, poorly designed idle loops can cause the system to double its energy consumption—energy that could be saved by a simple hardware sleep mechanism

Fine mapping and expression of candidate genes within the chromosome 10 QTL region of the high and low alcohol-drinking rats

The high and low alcohol-drinking (HAD and LAD) rats were selectively bred for differences in alcohol intake. The HAD/LAD rats originated from the N/Nih heterogeneous stock developed from intercrossing eight inbred rat strains. The HAD×LAD F2 were genotyped, and a powerful analytical approach, using ancestral recombination and F2 recombination, was used to narrow a quantitative trait loci (QTL) for alcohol drinking to a 2-cM region on distal chromosome 10 that was in common in the HAD1/LAD1 and HAD2/LAD2 analyses. Quantitative real-time PCR was used to examine mRNA expression of six candidate genes (Crebbp, Trap1, Gnptg, Clcn7, Fahd1, and Mapk8ip3) located within the narrowed QTL region in the HAD1/LAD1 rats. Expression was examined in five brain regions, including the nucleus accumbens, amygdala, caudate putamen, hippocampus, and prefrontal cortex. All six genes showed differential expression in at least one brain region. Of the genes tested in this study, Crebbp and Mapk8ip3 may be the most promising candidates with regard to alcohol drinking

Numerical investigation of the high pressure selective catalytic reduction system impact on marine two-stroke diesel engines

After-treatment systems using the selective catalytic reduction (SCR) technology have demonstrated a potential to reduce the nitrogen oxides (NOx) emissions from marine engines by more than 90% with its most typical configurations being the high pressure system (SCR-HP) and the low pressure system (SCR-LP). This study aims to investigate the impact of the SCR-HP system on a large marine two-stroke engine performance parameters by employing thermodynamic modelling. A coupled model of the zero-dimensional type is extended to incorporate the modelling of the SCR-HP system components and the control bypass valve (CBV) block. The CBV control system is modelled based on the exhaust gas minimum temperature set point, which is considered a function of the sulphur content and the exhaust receiver pressure. This model is initially validated against experimental data and subsequently employed to simulate several scenarios representing the engine operation at both healthy and degraded conditions considering the compressor fouling and the SCR reactor clogging. The derived results are analysed to quantify the impact of the SCR-HP system on the investigated engine performance. The SCR system pressure drop and the cylinder bypass valve flow cause an increase of the engine specific fuel oil consumption (SFOC) in the range 0.3 to 2.77 g/kWh. The thermal inertia of the SCR-HP system is mainly attributed to the SCR reactor, which causes a delayed turbocharger response. These effects are more pronounced at low engine loads. This study supports the better understanding of the operating characteristics of marine two-stroke diesel engines equipped with the SCR-HP system and quantification of the impact of the components degradation on the engine performance. Furthermore, it provides insights for the effective shipboard operation of these engines and the SCR-HP system

Estrogen-Dependent Upregulation of Adcyap1r1 Expression in Nucleus Accumbens Is Associated With Genetic Predisposition of Sex-Specific QTL for Alcohol Consumption on Rat Chromosome 4

Humans show sex differences related to alcohol use disorders (AUD). Animal model research has the potential to provide important insight into how sex differences affect alcohol consumption, particularly because female animals frequently drink more than males. In previous work, inbred strains of the selectively bred alcohol-preferring (P) and non-preferring (NP) rat lines revealed a highly significant quantitative trait locus (QTL) on rat chromosome 4, with a logarithm of the odds score of 9.2 for alcohol consumption. Recently, interval-specific congenic strains (ISCS) were developed by backcrossing the congenic P.NP line to inbred P (iP) rats to further refine the chromosome 4 QTL region. Two ISCS sub-strains, ISCS-A and ISCS-B, were obtained with a narrowed QTL, where the smallest region of overlap consisted of 8.9 Mb in ISCS-B. Interestingly, we found that females from both ISCS lines consumed significantly less alcohol than female iP controls (p < 0.05), while no differences in alcohol consumption were observed between male ISCS and iP controls. RNA-sequencing was performed on the nucleus accumbens of alcohol-naïve female ISCS-B and iP rats, which revealed differentially expressed genes (DEG) with greater than 2-fold change and that were functionally relevant to behavior. These DEGs included down-regulation of Oxt, Asb4, Gabre, Gabrq, Chat, Slc5a7, Slc18a8, Slc10a4, and Ngfr, and up-regulation of Ttr, Msln, Mpzl2, Wnt6, Slc17a7, Aldh1a2, and Gstm2. Pathway analysis identified significant alterations in gene networks controlling nervous system development and function, as well as cell signaling, GABA and serotonin receptor signaling and G-protein coupled receptor signaling. In addition, β-estradiol was identified as the most significant upstream regulator. The expression levels of estrogen-responsive genes that mapped to the QTL interval and have been previously associated with alcohol consumption were measured using RT-qPCR. We found that expression of the Adcyap1r1 gene, encoding the pituitary adenylate cyclase-activating polypeptide type 1 (PAC1) receptor, was upregulated in female ISCS-B compared to female iP controls, while no differences were exhibited in males. In addition, sequence variants in the Adcyap1r1 promoter region showed a differential response to estrogen stimulation in vitro. These findings demonstrate that rat chromosome 4 QTL contains genetic variants that respond to estrogen and are associated with female alcohol consumption

Influence factors and reasonable arrangement of corridor width of ±800 kV HVDC and 750 kV HVAC hybrid transmission lines

With the development of economy and the increased demand of power energy, it is unavoidable that high-voltage direct current (HVDC) and high-voltage alternating current (HVAC) transmission lines are in the same corridor. In order to minimise the land resource and meet the requirements of the electromagnetic environment, it is necessary to accurately predict the hybrid electric field under the hybrid transmission lines. The ±800 kV HVDC and 750 kV HVAC parallel transmission lines of parallel erection are chosen to be analysed. The corridor width with a different separation distance is calculated, and the minimum corridor width under this voltage-level combination is obtained according to the control value of the hybrid electric field recommended at home and abroad in a non-residential area. Increasing the height of DC or AC lines can reduce the corridor width. At a fixed separation distance, the minimum height of the AC line can be obtained when the height of the DC line is set at a certain value. Meanwhile the change of the corridor width is analysed with different heights of DC lines and AC lines. Based on the above analysis, the reasonable arrangement is made