Commencement Program, May (1987)

https://red.mnstate.edu/commencement/1145/thumbnail.jp

Intrinsic mechanical behavior of MgAgSb thermoelectric material: An ab initio study

α-MgAgSb based thermoelectric (TE) device attracts much attention for its commercial application because it shows an extremely high conversion efficiency of ∼8.5% under a temperature difference of 225 K. However, the mechanical behavior of α-MgAgSb is another serious consideration for its engineering applications. Here, we apply density functional theory (DFT) simulations to examine the intrinsic mechanical properties of all three MgAgSb phases, including elastic properties, shear-stress – shear-strain relationships, deformation and failure mechanism under ideal shear and biaxial shear conditions. We find that the ideal shear strength of α-MgAgSb is 3.25 GPa along the most plausible (100) slip system. This strength is higher than that of β-MgAgSb (0.80 GPa) and lower than that of γ-MgAgSb (3.43 GPa). The failure of α-MgAgSb arises from the stretching and breakage of Mg-Sb bond α-MgAgSb under pure shear load, while it arises from the softening of Mg-Ag bond and the breakage of Ag-Sb bond under biaxial shear load. This suggests that the deformation mechanism changes significantly under different loading conditions

Auto-correlative weak-value amplification under strong noise background

In the general optical metro-logical protocols based on the weak-value amplification(WVA) approach, it is beneficial to choose the pre-selected state and the post-selected one to be nearly orthogonal for improving the sensitivity. However, the orthogonality of the post-selection decreases the probability of detecting photons and makes the weak measurement difficult, especially when there is strong noise background and the pointer is drowned in noise. In this article, we investigate a modified weak measurement protocol with a temporal pointer, namely, the auto-correlative weak-value amplification (AWVA) approach. We find it can significantly improve the precision of optical metrology under Gaussian white noise, especially with a negative signal-to-noise ratio. With the AWVA approach, a small longitudinal time delay (tiny phase shift) $\tau$ of a Gaussian pulse is measured by implementing two auto-correlative weak measurements. The small quantities are obtained by measuring the auto-correlation coefficient of the pulses instead of fitting the shift of the mean value of the probe. Simulation results show that the AWVA approach outperforms the standard WVA technique in the time domain, remarkably increasing the precision of weak measurement under strong noise background.Comment: 15 pages, 10 figure

Ductile deformation mechanism in semiconductor α-Ag_(2)S

Inorganic semiconductor α-Ag2S exhibits a metal-like ductile behavior at room temperature, but the origin of this high ductility has not been fully explored yet. Based on density function theory simulations on the intrinsic mechanical properties of α-Ag2S, its underlying ductile mechanism is attributed to the following three factors: (i) the low ideal shear strength and multiple slip pathways under pressure, (ii) easy movement of Ag–S octagon framework without breaking Ag−S bonds, and (iii) a metallic Ag−Ag bond forms which suppresses the Ag–S frameworks from slipping and holds them together. The easy slip pathways (or easy rearrangement of atoms without breaking bonds) in α-Ag2S provide insight into the understanding of the plastic deformation mechanism of ductile semiconductor materials, which is beneficial for devising and developing flexible semiconductor materials and electronic devices

Seminal Plasma Metabolome in Relation to Semen Quality and Urinary Phthalate Metabolites Among Chinese Adult Men

Background: A growing body of evidence has found links between endocrine disruptor phthalates and male reproductive disorders, but the mechanisms underlying these relationships are poorly known. Seminal plasma metabolomes may mediate associations of phthalate exposure with impaired semen quality. Objective: To identify seminal plasma metabolomes associated with poor semen quality and evaluate their associations with urinary phthalate metabolites among 660 Chinese adult men. Method: The seminal plasma metabolic profiles were acquired using an untargeted approach based on liquid chromatography-high resolution mass spectrometry. We explored the differences in seminal plasma metabolites between participants with poor and good semen quality and evaluated cross-sectional associations between discriminatory metabolic biomarkers and urinary phthalate metabolites. Results: Differences between poor and good semen quality groups were observed in relation to 25 seminal plasma metabolites, mostly related to the metabolism of polyunsaturated fatty acids (PUFA) and acylcarnitine (all p \u3c 0.05). After adjusting for various confounders and multiple tests, metabolites were all significantly associated with one or more individual sperm quality parameters (motility, concentration, total count, and morphology) (all p \u3c 0.05). Among identified metabolic biomarkers, seminal plasma L-palmitoylcarnitine, linoelaidyl carnitine, and oleic acid were inversely associated with urinary mono-(2-ethylhexyl) phthalate (MEHP), and seminal plasma L-acetylcarnitine was inversely associated with the proportion of di-(2-ethylhexyl)-phthalate metabolites (DEHP) excreted as MEHP in urine (%MEHP) (all p \u3c 0.05). Mediation analysis revealed that oleic acid and L-acetylcarnitine mediated significant proportions (6.7% and 17%, respectively) of the positive associations between urinary DEHP metabolites and the percentage of spermatozoa with an abnormal head. Conclusions: Elevated urinary phthalate metabolites may impact semen quality by causing metabolic disorders of seminal plasma PUFAs and acylcarnitine. These pathways warrant further investigation

Ductile deformation mechanism in semiconductor α-Ag_(2)S

Inorganic semiconductor α-Ag2S exhibits a metal-like ductile behavior at room temperature, but the origin of this high ductility has not been fully explored yet. Based on density function theory simulations on the intrinsic mechanical properties of α-Ag2S, its underlying ductile mechanism is attributed to the following three factors: (i) the low ideal shear strength and multiple slip pathways under pressure, (ii) easy movement of Ag–S octagon framework without breaking Ag−S bonds, and (iii) a metallic Ag−Ag bond forms which suppresses the Ag–S frameworks from slipping and holds them together. The easy slip pathways (or easy rearrangement of atoms without breaking bonds) in α-Ag2S provide insight into the understanding of the plastic deformation mechanism of ductile semiconductor materials, which is beneficial for devising and developing flexible semiconductor materials and electronic devices

Determining ideal strength and failure mechanism of thermoelectric CuInTe_2 through quantum mechanics

CuInTe_2 is recognized as a promising thermoelectric material in the moderate temperature range, but its mechanical properties important for engineering applications remain unexplored so far. Herein, we applied quantum mechanics (QM) to investigate such intrinsic mechanical properties such as ideal strength and failure mechanism along with pure shear, uniaxial tension, and biaxial shear deformations. We found that the ideal shear strength of CuInTe_2 is 2.43 GPa along the (221)[11−1] slip system, which is much lower than its ideal tensile strength of 4.88 GPa along [1−10] in tension, suggesting that slipping along (221)[11−1] is the most likely activated failure mode under pressure. Shear induced failure of CuInTe_2 arises from softening and breakage of the covalent In–Te bond. However, tensile failure arises from breakage of the Cu–Te bond. Under biaxial shear load, compression leads to shrinking of the In–Te bond and consequent buckling of the In–Te hexagonal framework. We also found that the ideal strength of CuInTe_2 is relatively low among important thermoelectric materials, indicating that it is necessary to enhance the mechanical properties for commercial applications of CuInTe_2

Determining ideal strength and failure mechanism of thermoelectric CuInTe_2 through quantum mechanics

CuInTe_2 is recognized as a promising thermoelectric material in the moderate temperature range, but its mechanical properties important for engineering applications remain unexplored so far. Herein, we applied quantum mechanics (QM) to investigate such intrinsic mechanical properties such as ideal strength and failure mechanism along with pure shear, uniaxial tension, and biaxial shear deformations. We found that the ideal shear strength of CuInTe_2 is 2.43 GPa along the (221)[11−1] slip system, which is much lower than its ideal tensile strength of 4.88 GPa along [1−10] in tension, suggesting that slipping along (221)[11−1] is the most likely activated failure mode under pressure. Shear induced failure of CuInTe_2 arises from softening and breakage of the covalent In–Te bond. However, tensile failure arises from breakage of the Cu–Te bond. Under biaxial shear load, compression leads to shrinking of the In–Te bond and consequent buckling of the In–Te hexagonal framework. We also found that the ideal strength of CuInTe_2 is relatively low among important thermoelectric materials, indicating that it is necessary to enhance the mechanical properties for commercial applications of CuInTe_2