Speed-dependent mean force and fluctuations between fluid-immersed PDMS surfaces upon sliding

In our previous work on shear flows of densely packed PDMS(dimethicone) particles, we have found that the system exhibits an transition zone of driving rates, and interpreted the behaviors as consequences of the speed-dependent friction between particles. To provide solid supports for the interpretation, we set a force balance for time-resolving the contact force between two curved PDMS surfaces that are sliding against each other. Two types of experiments include the passing of two semi-spheres, and the sliding with a sustained contact between two orthogonal semi-cylinders of which one is moving at a controlled speed $U$ with a fixed depth of compression $D_p$ into the other. For sphere-passing experiments, the tangential force reveals a characteristic speed $V_c$, beyond which the time-averaged value decays substantially with the increase of $U$, whereas the normal force shows no detectable change. The characteristic speed $V_c$ appears insensitive to the change of $D_p$ and subsequently to the normal force. Data from experiments with a sustained contact follow the similar trend. We have also verified that the normal force shows a dependence on $D_p$ with a Hertzian scaling. Varying the viscosity $\eta$ by two decades lead to shifts of the speed dependence and we find that $\kappa\equiv\eta U$ provides a good collapse of data, in consistence with prior studies. In addition, we study the fluctuation of tangential force over time. We have found that prominent stick-slip patterns occur only at sufficiently high driving speeds. The change of pattern suggests a change from a regime with sustained solid-to-solid contact, to that of mixed lubrication where the direct contact is intermittent. Detailed analyses on the fluctuations reveal a high sensitivity to surface condition, presumably due to factors such as long-time absorption of molecules, the effects of wearing, or a combination of both

Online Self-Concordant and Relatively Smooth Minimization, With Applications to Online Portfolio Selection and Learning Quantum States

Consider an online convex optimization problem where the loss functions are self-concordant barriers, smooth relative to a convex function $h$, and possibly non-Lipschitz. We analyze the regret of online mirror descent with $h$. Then, based on the result, we prove the following in a unified manner. Denote by $T$ the time horizon and $d$ the parameter dimension. 1. For online portfolio selection, the regret of $\widetilde{\text{EG}}$, a variant of exponentiated gradient due to Helmbold et al., is $\tilde{O} ( T^{2/3} d^{1/3} )$ when $T > 4 d / \log d$. This improves on the original $\tilde{O} ( T^{3/4} d^{1/2} )$ regret bound for $\widetilde{\text{EG}}$. 2. For online portfolio selection, the regret of online mirror descent with the logarithmic barrier is $\tilde{O}(\sqrt{T d})$. The regret bound is the same as that of Soft-Bayes due to Orseau et al. up to logarithmic terms. 3. For online learning quantum states with the logarithmic loss, the regret of online mirror descent with the log-determinant function is also $\tilde{O} ( \sqrt{T d} )$. Its per-iteration time is shorter than all existing algorithms we know.Comment: 19 pages, 1 figur

Spontaneous Arrangement of Two-way Flow in Water Bridge

By revisiting the century-old problem of water bridge, we demonstrate that it is in fact dynamic and comprises of two coaxial currents that carry different charges and flow in opposite directions. Initially, the inner flow is facilitated by the cone jet that is powered by H+ and flows out of the anode beaker. The negative cone jet from cathode is established later and forced to take the outer route. This spontaneous arrangement of two-way flow is revealed by the use of chemical dyes, e.g., fluorescein and FeCl3, carbon powder, and the Particle Image Velocimetry. These two opposing flows are found to carry non-equal flux that results in a net transport of water to the cathode beaker. By combining the above information and taking into account the counter flow to equate the water level from the connecting pipe, we can estimate the cross section and flow speed of these co-axial flows as a function of time and applied voltage.Comment: 5 pages, 5 figure

State diagram for packed granular particles under shear: two types of /quaking/ and "shear unjamming"

Understanding intermittency, an ubiquitous behavior in flows of packed grains, is pivotal for establishing the rheology of granular material. A straightforward explanation has been missing despite the long development of theories at different levels of abstraction. In this work, we propose the use of a Stribeck-Hertz model that starts with the classic Coulomb friction but also takes into account the tribology between particles, i.e. the reduction of friction coefficient with speed as is commonly observed. Our numerical studies reveal a state diagram covering a wide range of packing fractions, and produce the quaking intermittency in the mid-range of a dimensionless shear rate defined accordingly, in consistence with our recent experimental observation [Phys. Rev. Lett. 126.128001 (2021)]. Monitoring the change of mean contact number allows us to distinguish two types of quaking. Above the random-close-packing density, the quakes are exclusively of the first type, occurred with a sudden increase of the contact number. At lower packing fractions, the dominant quaking depends in part on the dimensionless shear rate. The second type of quaking is identified as the prelude for a granular packing to "unjam" upon increase of the dimensionless shear rate -- a phenomenon that occurs only when the essential tribology is taken into accoun

Recycling Nonmagnetic Material from De-sulferization Slag as Coarse Aggregate through Cold-Pressing Technique

Every year there was approximately 500,000 tons of de-sulferization slag generated in Taiwan, but the recycling amount was very slightly. A new approach, the cold-pressing technique that incorporates the principles of the cement chemistry and composite material was developed to recycle innocuous resources (e.g. construction residual soil, granite and lime sludge, and sediment, etc.) as recycling coarse aggregate. Even this technique also has successfully been applied to recycle stainless steel reductive slag with low volume stability. This paper aims to show that using cold-pressing technique can recycle nonmagnetic material from de-sulferization slag as coarse aggregate. Herein the cement-based composite is regarded as concrete. Particularly, the mixture proportions with a low cement amount of 100 kg/m3 and more than 70% (by weight) of nonmagnetic material from de-sulferization were designed. The test results show that the specific gravity of recycling coarse aggregate is about 1.67 in the OD state; the absorption capacity is 27.65%; the dry loose density (i.e. unit weight) is about 1,106 kg/m3; and other characteristics conform to ASTM C33. Therefore the cold-pressing technique is a new and practicable approach to recycle nonmagnetic material from de-sulferization slag in future

Granzyme G is expressed in the two-cell stage mouse embryo and is required for the maternal-zygotic transition

<p>Abstract</p> <p>Background</p> <p>Detailed knowledge of the molecular and cellular mechanisms that direct spatial and temporal gene expression in pre-implantation embryos is critical for understanding the control of the maternal-zygotic transition and cell differentiation in early embryonic development. In this study, twenty-three clones, expressed at different stages of early mouse development, were identified using differential display reverse transcription polymerase chain reaction (DDRT-PCR). One of these clones, which is expressed in 2-cell stage embryos at 48 hr post-hCG injection, shows a perfect sequence homology to the gene encoding the granzyme G protein. The granzyme family members are serine proteases that are present in the secretory granules of cytolytic T lymphocytes. However, the pattern of granzyme G expression and its function in early mouse embryos are entirely unknown.</p> <p>Results</p> <p>Upon the introduction of an antisense morpholino (2 mM) against granzyme G to knock-down endogenous gene function, all embryos were arrested at the 2- to 4-cell stages of egg cleavage, and the <it>de novo </it>synthesis of zygotic RNAs was decreased. The embryonic survival rate was dramatically decreased at the late 2-cell stage when serine protease-specific inhibitors, 0.1 mM 3,4-dichloroisocoumarin (3,4-DCI), and 2 mM phenyl methanesulphonyl fluoride (PMSF), were added to the <it>in vitro </it>embryonic culture medium. Survival was not affected by the addition of 0.5 mM EDTA, a metalloproteinase inhibitor.</p> <p>Conclusion</p> <p>We characterized for the first time the expression and function of <it>granzyme G </it>during early stage embryogenesis. Our data suggest that granzyme G is an important factor in early mouse embryonic development and may play a novel role in the elimination of maternal proteins and the triggering of zygotic gene expression during the maternal-zygotic transition.</p

Serotonin receptor HTR6-mediated mTORC1 signaling regulates dietary restriction-induced memory enhancement

Dietary restriction (DR; sometimes called calorie restriction) has profound beneficial effects on physiological, psychological, and behavioral outcomes in animals and in humans. We have explored the molecular mechanism of DR-induced memory enhancement and demonstrate that dietary tryptophan-a precursor amino acid for serotonin biosynthesis in the brain-and serotonin receptor 5-hydroxytryptamine receptor 6 (HTR6) are crucial in mediating this process. We show that HTR6 inactivation diminishes DR-induced neurological alterations, including reduced dendritic complexity, increased spine density, and enhanced long-term potentiation (LTP) in hippocampal neurons. Moreover, we find that HTR6-mediated mechanistic target of rapamycin complex 1 (mTORC1) signaling is involved in DR-induced memory improvement. Our results suggest that the HTR6-mediated mTORC1 pathway may function as a nutrient sensor in hippocampal neurons to couple memory performance to dietary intake

中正嶺學報 第三十五卷 第一期 民國95.11

ABSTRACT The regression curve, obtained for project control of large-scale or small-scale engineering, is smoothly connected by a Takagi-Sugeno fuzzy model. A sample of data taken from Department of Rapid Transit Systems, Taipei City Government is used to demonstrate the concept of the proposed regression model using statistical method. This developed S-curve equation could be used in a variety of applications related to project control in the working capital management of construction firms