לוח שנה משולב

Dye sensitized solar cells (DSSC), are low cost alternative to traditional silicon solar cells. Upon illumination the dye absorbs photons, and goes to excited state generating electron and hole pairs. The electrons are injected into the TiO2 conduction band and diffuse to the front contact, simultaneously the holes are injected into redox couple. This work will discuss three crucial topics for improving DSSC performance. (i) Replacing the organic dye molecules (sensitizer) by quantum dots (QDs), which have several advantages over the dye molecules. Semiconductor QDs belonging to group IV-VI, such as PbS and PbSe, are known as good absorbers in the visible and in the near IR regime. They have relatively large ground state cross-section of absorption, long excitonic lifetime, and exceptionally high quantum efficiency of the luminescence. A highly efficient solid state PbS (QDs)/TiO2 heterojunction solar cell will be presented. Importantly, the PbS QDs act here as photosensitizers and at the same time as hole conductors. Therefore no hole conductor is necessary in this type of cell. (ii) Changing the photo-anode (working electrode) of the DSSC using ZnO Nanowires (NWs), which were grown on conductive fluorine doped tin oxide glass. The combination of ZnO NWs with newly developed organic dye shows high power conversion efficiency. (iii) In DSSC a liquid electrolyte (usually iodide/triiodide in acetonitrile) is used, but the presence of organic solvents poses problems for practical implementation. In this topic the liquid electrolyte was replaced with radically new solid-state (or quasi-solid) conductors, in order to reduce potential environmental risks and ensure much greater stability in outdoor operating conditions. Nanomaterials with a porous or layered structure were used, those materials employed a high specific surface area and complex engineered architectures in order to host redox active species.

While stars have been historically considered to be eternal, we now know that some stars become un-stable and explode, producing dazzling cosmic fireworks shows. These events turn out to be very useful natural laboratories, where we can study fundamental physical processes extending from the smallest particle physics scales; nuclear physics questions like the origin of the elements; general relativity and gravitation in the strong field limit; and out to the largest cosmological scales of the Universe as a whole. I will review the various physical mechanisms that lead to the explosive death of stars as supernova ex-plosions, the progress we made during the last few years in understanding these events, and the pro-spects for further advances driven by new technologies.

Nanoscale engineering is one of the most dynamically growing areas in science and industry. As there are no safety regulations yet, concerns about future health problems are mounting. The fundamental question that arises is, whether size alone can be detrimental. In order to investigate this issue, one must study the effects of both inert i.e. noble metal (1,3) and chemically active (Ti and Zn oxide) nanoparticles (2).
Living tissues are composed of a hierarchy of cell structures, where each layer had a unique cell type and function. In order to understand the effects of nanoparticles living organisms it is important to study cells from primary cultures and determine, not only the concentrations that would induce apoptosis, but rather the effects of the particles on specific cell functions. Since the different cell layers are interconnected a reduction in function on any one of the layers can impact the development of the rest of the tissue.
Here I will focus on studies which examine the impact of the nanoparticles on the function of various types of primary culture skin cells. Skin tissue is chosen as a model since it is the first barrier to penetration from contact type of exposure. We found that, even at very low concentrations, where no apoptosis was detected, both types of particles were capable of interfering with normal cell functions such as migration, proliferation, and ECM formation. In the case of inert particles, a critical concentration existed below which recovery was possible if the source of particles was removed. Other particles, such as montmorilonite clays, whose large aspect ratio prevented cell penetration, were found to have beneficial impact on cell growth and proliferation. In the case of the photoactive particles, their effects in the absence and presence of UV exposure is explored.
For the reactive particles, special coatings could be synthesized which prevented penetration and damage. Since the coatings can be made from REACH compliant materials, they can be used in personal care products and cosmetics (2).

1. Adverse effects of citrate/gold nanoparticles on human dermal fibroblasts Pernodet N, Fang XH, Sun Y, Bakhtina A, Ramakrishnan A, Sokolov J, Ulman A, Rafailovich M. Small 2006 2 (6): 766-773
2. Multicomponent polymer coating to block photocatalytic activity of TiO2 nanoparticles, Wilson A. Lee,
Nadine Pernodet, Bingquan Li, Chien H. Lin, Eli Hatchwell and Miriam H. Rafailovich, Chemical
Communications (2007) Pages: 4815-4817
3. Gold nanoparticles cellular toxicity and recovery: Effect of size, concentration and exposure time
Tatsiana Mironava, Michael Hadjiargyrou, Marcia Simon, Vladimir Jurukovski, Miriam H. Rafailovich
Nanotoxicology Mar 2010, Vol. 4, No. 1: 120–137

The earliest time in the history of the universe that is clearly probed by observations is the period from about one second to about five minutes after the big bang, when the initial chemical composition of the universe was determined in the process known as big-bang nucleosynthesis (BBN). This was a much simpler time than today, so the physical processes that produced measurable amounts of only hydrogen, helium, and lithium can be easily modeled. By studying the isotopic compositions of the light elements and comparing against the model, we learn about both the overall structure of the universe and the fundamental particles that populate it. I will review the theory and observational evidence regarding BBN, as well as their relation to other cosmological measurements. I will then discuss recent results concerning elementary-particle properties and the surprisingly loose limits on large-scale inhomogeneities in the primordial distribution of matter. Finally, I will examine some lingering difficulties with BBN.
Throughout the discussion I will emphasize the important role of the physics of light nuclei in formulating BBN as a high-precision theory.