Weizmann Institute of Science

About: Weizmann Institute of Science is a education organization based out in Rehovot, Israel. It is known for research contribution in the topics: Population & Gene. The organization has 21942 authors who have published 54561 publications receiving 3032812 citations. The organization is also known as: Bessie F. Lawrence International Summer Science Institute & Weitzman Institute.

Hollow nanoparticles of WS2 as potential solid-state lubricants

Abstract: Solid lubricants fill a special niche in reducing wear in situations where the use of liquid lubricants is either impractical or inadequate, such as in vacuum, space technology or automotive transport. Metal dichalcogenides MX2 (where M is, for instance, Mo or W and X is S or Se) are widely used as solid lubricants. These materials are characterized by a layered structure with weak (van der Waals) inter-layer forces that allow easy, low-strength shearing1,2. Within the past few years, hollow nanoparticles (HNs) of MX2 with structures similar to those of nested carbon fullerenes and nanotubes have been synthesized3,4. Here we show that these materials can act as effective solid lubricants: HN-WS2 outperforms the solid lubricants 2H-MoS2 and 2H-WS2 in every respect (friction, wear and lifetime of the lubricant) under varied test conditions. We attribute the outstanding performance of HN-WS2 to its chemical inertness and the hollow cage structure, which imparts elasticity and allows the particles to roll rather than to slide.

Protein production and purification.

Abstract: In selecting a method to produce a recombinant protein, a researcher is faced with a bewildering array of choices as to where to start. To facilitate decision-making, we describe a consensus 'what to try first' strategy based on our collective analysis of the expression and purification of over 10,000 different proteins. This review presents methods that could be applied at the outset of any project, a prioritized list of alternate strategies and a list of pitfalls that trip many new investigators.

Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells

Abstract: THE non-biological reduction of carbon dioxide to organic compounds is of interest, as an alternative to natural photosynthesis, for the production of organic raw materials or fuel. In one approach, the required energy was supplied by irradiation with UV light, in the presence of ferrous salts, and resulted in the production of formic acid and of formaldehyde1. In another approach, the energy was supplied from an external power source by electrochemical reduction of aqueous carbon dioxide. The reduction of carbon dioxide and production of formic acid during the electrolysis of sodium bicarbonate in aqueous solutions has also been reported2, and a study of the reduction of carbon dioxide on a mercury cathode reviews earlier work3. Polarographic measurements on mercury electrodes showed that carbon dioxide, rather than the bicarbonate ion, is the electroactive species, with a half-wave reduction potential of −2.1 V (relative to SCE), and that formic acid is the only product4. We report here the photoassisted electrolytic reduction of aqueous carbon dioxide, achieved using p-type gallium phosphide as a photocathode, with part or all of the energy being supplied by light. The products were formic acid, formaldehyde and methanol.

Scaling limits of loop-erased random walks and uniform spanning trees

Abstract: The uniform spanning tree (UST) and the loop-erased random walk (LERW) are related probabilistic processes. We consider the limits of these models on a fine grid in the plane, as the mesh goes to zero. Although the existence of scaling limits is still unproven, subsequential scaling limits can be defined in various ways, and do exist. We establish some basic a.s. properties of the subsequential scaling limits in the plane. It is proved that any LERW subsequential scaling limit is a simple path, and that the trunk of any UST subsequential scaling limit is a topological tree, which is dense in the plane. The scaling limits of these processes are conjectured to be conformally invariant in 2 dimensions. We make a precise statement of the conformal invariance conjecture for the LERW, and show that this conjecture implies an explicit construction of the scaling limit, as follows. Consider the Loewner differential equation ${\partial f\over\partial t} = z {\zeta(t)+z \over \zeta(t)-z} {\partial f\over\partial z}$ with boundary values $f(z,0)=z$, in the range $z\in\U=\{w\in\C\st |w|<1\}$, $t\le 0$. We choose $\zeta(t):= \B(-2t)$, where $\B(t)$ is Brownian motion on $\partial \U$ starting at a random-uniform point in $\partial \U$. Assuming the conformal invariance of the LERW scaling limit in the plane, we prove that the scaling limit of LERW from 0 to $\partial\U$ has the same law as that of the path $f(\zeta(t),t)$. We believe that a variation of this process gives the scaling limit of the boundary of macroscopic critical percolation clusters.