פרסומים

In a previous communication (Kindt et al., 2001) we reported preliminary results of Brownian dynamics simulation and analytical theory which address the packaging and ejection forces involving DNA in bacteriophage capsids. In the present work we provide a systematic formulation of the underlying theory, featuring the energetic and structural aspects of the strongly confined DNA. The free energy of the DNA chain is expressed as a sum of contributions from its encapsidated and released portions, each expressed as a sum of bending and interstrand energies but subjected to different boundary conditions. The equilibrium structure and energy of the capsid-confined and free chain portions are determined, for each ejected length, by variational minimization of the free energy with respect to their shape profiles and interaxial spacings. Numerical results are derived for a model system mimicking the lambda-phage. We find that the fully encapsidated genome is highly compressed and strongly bent, forming a spool-like condensate, storing enormous elastic energy. The elastic stress is rapidly released during the first stage of DNA injection, indicating the large force (tens of pico Newtons) needed to complete the (inverse) loading process. The second injection stage sets in when similar to1/3 of the genome has been released, and the interaxial distance has nearly reached its equilibrium value (corresponding to that of a relaxed torus in solution); concomitantly the encapsidated genome begins a gradual morphological transformation from a spool to a torus. We also calculate the loading force, the average pressure on the capsid’s walls, and the anisotropic pressure profile within the capsid. The results are interpreted in terms of the (competing) bending and interaction components of the packing energy, and are shown to be in good agreement with available experimental data.

Gender gaps in physics in favour of boys are more prominent in Israel than in other countries. The main research question is to find out what gender issues are at play in Israeli advanced placement physics classes. Matriculation exam scores from approximately 400 high schools were analysed across 12 years. In addition, semi-constructed interviews were conducted with 50 advanced placement physics students (25 girls and 25 boys). In terms of participation, it was found that the ratio of girls to boys has been unchanged from 1988 to 2000 and is roughly 1:3. In terms of performance, it was found that the final matriculation scores of boys and girls are similar. However, breaking up the final scores into its two components - teachers’ given grades and matriculation test scores - showed that boy’s test scores are usually higher than girls’ test scores, while girls’ teachers’ given grades are usually higher than boys’. Results from semi-constructed interviews pointed to two factors that are especially unfavourable to many girls: excessive competitiveness and lack of teaching for understanding. Girls’ yearning for deep understanding is seen as a form of questing for connected knowledge. It is suggested that instructional methods that foster students’ understanding while decreasing competitiveness in physics classes might contribute to girls’ participation and performance in advanced physics classes while also supporting the learning of many boys.

Gender gaps in physics in favour of boys are more prominent in Israel than in other countries. The main research question is to find out what gender issues are at play in Israeli advanced placement physics classes. Matriculation exam scores from approximately 400 high schools were analysed across 12 years. In addition, semi-constructed interviews were conducted with 50 advanced placement physics students (25 girls and 25 boys). In terms of participation, it was found that the ratio of girls to boys has been unchanged from 1988 to 2000 and is roughly 1:3. In terms of performance, it was found that the final matriculation scores of boys and girls are similar. However, breaking up the final scores into its two components - teachers' given grades and matriculation test scores - showed that boy's test scores are usually higher than girls' test scores, while girls' teachers' given grades are usually higher than boys'. Results from semi-constructed interviews pointed to two factors that are especially unfavourable to many girls: excessive competitiveness and lack of teaching for understanding. Girls' yearning for deep understanding is seen as a form of questing for connected knowledge. It is suggested that instructional methods that foster students' understanding while decreasing competitiveness in physics classes might contribute to girls' participation and performance in advanced physics classes while also supporting the learning of many boys.

Fostering students’ higher order thinking skills is considered an important educational goal. Although learning theories see the development of students’ thinking as an important goal for all students, teachers often believe that stimulating higher order thinking is appropriate only for high-achieving students. According to this view, low-achieving students are, by and large, unable to deal with tasks that require higher order thinking skills and should thus be spared the frustration generated by such tasks. Because this view may cause teachers to treat students in a nonegalitarian way, it is important to find out whether or not it is supported by empirical evidence. The goal of this study is to examine this issue in light of four different studies, by asking the following question: Do low-achieving students gain from teaching and learning processes that are designed to foster higher order thinking skills? Each of the4 studies addressed a different project whose goal was to teach higher order thinking in science classrooms. Following a brief general description of each project, we provide an analysis of its effects on students with low and high achievements. The findings show that by the end of each of the 4 programs, students with high academic achievements gained higher thinking scores than their peers with low academic achievements. However, students of both subgroups made considerable progress with respect to their initial score. In one of the 4 studies the net gain of low achievers was significantly higher than for high achievers. Our findings strongly suggest that teachers should encourage students of all academic levels to engage in tasks that involve higher order thinking skills.

The formation of amorphous calcium phosphate (ACP) and its transformation into octacalcium phosphate (OCP) in the presence of poly-l-glutamic acid (PGA, Mw 3 000 D and 50 000 D), poly-l-lysine (PLL, Mw 50 000 D) and polystyrene sulfonate (PSS, MW 70 000 D) has been investigated. All polyelectrolytes at low concentrations induced and at high concentrations retarded nucleation of the crystalline precipitate. In addition, the polyelectrolytes inhibited aggregation of ACP particles and growth of the crystalline phase. The intensity of the effects depended on the charge, molecular mass, and concentration of the specific polymer.

Alcohols and polyols are essential components (in addition to the surfactant, water, and oil) in the formation of U-type self-assembled nano-structures, (sometimes called L-phases or U-type microemulsions). These microemulsions are characterized by large isotropic regions ranging from the oil side of the phase diagram up to the aqueous corner. The isotropic oily solutions of reverse micelles (''the concentrates'') can be diluted along some dilution lines with aqueous phase to the ``direct micelles'' corner via a bicontinuous mesophases (i.e., two structural transitions). This dilution takes place with no phase separations or occurrence of liquid crystalline phases. The structural transitions were determined by viscosity, conductivity, and pulsed gradient spin echo NMR (PGSE NMR), and are not visible to the eye. Two guest nutraceutical molecules (lutem and phytosterols) were solubilized, at their maximum solubilization capacity, in the reversed micellar solutions (L-2 phase) and were further diluted with the aqueous phase to the aqueous micellar comer (L-1 phase). Structural transitions (for the two types of molecule) from water-in-oil to bicontinuous microstructures were induced by the guest molecules. The transitions occurred at an earlier stage of dilution, at a lower water content (20 wt.% aqueous phase), than in the empty (blank) microemulsions (transitions at 30 wt.% aqueous phase). The transitions from the bicontinuous microstructure to the oilin-water microemulsions were retarded by the solubilizates and occurred at later dilution stage at higher aqueous phase contents (50 wt.% aqueous region for empty microemulsion and >60 wt.% for solubilized microemulsion). As a result, the bicontinuous isotropic region, in the presence of the guest molecules, becomes much broader. It seems that the main reason for such ``guest-induced structural transitions'' is related to a significant flattening and enhanced rigidity of the interface. The guest molecules of the high molecular volume are occupying high volume fraction of the interface (when the solubilization is maximal).

In this chapter some problems connected with the utilization of subzero temperature differential scanning calorimetry (SZT-DSC) are discussed. Among them are the determination of hydration numbers of surfactants and organic compounds, the determination of the hydration shell thickness, the effect of alcohol on the distribution of water between free and bound states in nonionic surfactant-based systems, and some considerations regarding the problem of phase separation of such systems in subzero temperatures. The significance of SZT-DSC for some novel applications is also discussed.

Winner of The Polonsky Prize for Creativity and Originality in the Humanistic Disciplines, The Hebrew University, 2004Avihu Zakai analyzes Jonathan Edwards’s redemptive mode of historical thought in the context of the Enlightenment. As theologian and philosopher, Edwards has long been a towering figure in American intellectual history. Nevertheless, and despite Edwards’s intense engagement with the nature of time and the meaning of history, there has been no serious attempt to explore his philosophy of history. Offering the first such exploration, Zakai considers Edwards’s historical thought as a reaction, in part, to the varieties of Enlightenment historical narratives and their growing disregard for theistic considerations.Zakai analyzes the ideological origins of Edwards’s insistence that the process of history depends solely on God’s redemptive activity in time as manifested in a series of revivals throughout history, reading this doctrine as an answer to the threat posed to the Christian theological teleology of history by the early modern emergence of a secular conception of history and the modern legitimation of historical time. In response to the Enlightenment refashioning of secular, historical time and its growing emphasis on human agency, Edwards strove to re-establish God’s preeminence within the order of time. Against the de-Christianization of history and removal of divine power from the historical process, he sought to re-enthrone God as the author and lord of history–and thus to re-enchant the historical world.Placing Edwards’s historical thought in its broadest context, this book will be welcomed by those who study early modern history, American history, or religious culture and experience in America. – Publisher’s Description

Major recent advances. Structured self-assembled liquids have been considered as efficient microreactors for organic and enzymatic reactions. Only recently scientists learned to use food-grade cosolvents and coemulsifiers together with hydrophilic non-ionic surfactants and to construct U-type phase diagrams with large isotropic regions ranging continuously from the oil-rich corner to the water-rich corner without any phase separation. The U-type microemulsions facilitate triggering and control of certain reactions by changing water activities. Maillard thermal degradation between sugars and amino acids is the main, and almost the only. chemical reaction that has been studied in food-grade microemulsions. Some examples of recent studies include: Maillard processes in binary structured fluids composed of monoglycerides of fatty acids and water forming microemulsions and lyotropic liquid crystalline structures; pseudoternary and pseudoquaternary W/O microemulsions; U-type microemulsions (W/O, O/W and bicontinuous microemulsions); enzymatic reactions aimed to prepare other surfactants such as sugar esters, monoglycerides and lysolecithins or triglycerides. Reactions in microreactors lead to unique new products. The reaction products and rates are controlled by the hydrophilicity/lipophilicity of the reagents (guest molecules), their molar ratios, type of oil phase, nature of surfactants and oil/surfactant ratios, nature of curvature and its elasticity (adjusted by cosolvent and coemulsifier) and by the water activity. The field is in its infancy and will need work of many more model reactions before it will be used in industrial food applications. Enzymatic reactions in non-food microemulsions are common practice but only few examples of food microemulsions as enzymatic microreactors have been extensively studied. (C) 2003 Elsevier Science Ltd. All rights reserved.

The microstructure of an unusual Winsor IV isotropic region of five-component microemulsions based on nonionic surfactants was studied. The microemulsions are composed of R(+)-limonene, water, propylene glycol (PG), ethanol (EtOH), and polyoxyethylene sorbitan monostearate (Tween 60) with a 1:1:3 R(+)limonene/ethanol/surfactant weight ratio. The phase diagrams of the system are characterized by an extended single continuous isotropic region starting from an oil-rich solution containing no aqueous phase (reverse micelles) to the water/propylene glycol (1/1) corner (swollen direct micelles). The microemulsions seem to be attractive for food applications. The microstructure changes gradually, smoothly, and continuously upon increasing the aqueous phase content. The microemulsion transforms from a water-in-oil (W/O) microemulsion to a bicontinuous phase and to an oil-in-water (O/W) microemulsion. The microstructure of the microemulsion along a selected dilution line, is probed using pulsed gradient spin-echo NMR, conductivity, and viscosity. The results are compared with a corresponding non-food-grade system based on C18:1E10 (Brij 96v). The hydrodynamic radius (R-H) of O/W microemulsion samples based on Brij 96v and Tween 60, at 90% aqueous phase, was determined to be 5.4 +/- 0.2 and 5.2 +/- 0.2 nm, respectively, and the calculated values of the area of the polar headgroup (a) are 87 for Brij 96v and 160 Angstrom(2) for Tween 60-based microemulsions. The ratio of the water self-diffusion coefficient, D-W, to the PG self-diffusion coefficient (D-PG) (termed the L ratio)was found to be sensitive to the aqueous phase content. In the O/W microemulsions, the water/PG mixture diffuses as hydrogen bonded entity (molecular diffusion controlled), while in the W/O microemulsions, the PG partitions, in part, at the interface and the dominate diffusion process is neither aggregate nor molecular controlled.

Osmotic shock is a familiar means for rupturing viral capsids and exposing their genomes intact. The necessary conditions for providing this shock involve incubation in high-concentration salt solutions, and lower permeability of the capsids to salt ions than to water molecules. We discuss here how values of the capsid strength can be inferred from calculations of the osmotic pressure differences associated with measured values of the critical concentration of incubation solution.

Analysis of the phenolic constituents of shea (Vitellaria paradoxa) kernels by LC-MS revealed eight catechin compounds-gallic acid, catechin, epicatechin, epicatechin gallate, gallocatechin, epigallocatechin, gallocatechin gallate, and epigallocatechin gallate-as well as quercetin and trans-cinnamic acid. The mean kernel content of the eight catechin compounds was 4000 ppm (0.4% of kernel dry weight), with a 2100-9500 ppm range. Comparison of the profiles of the six major catechins from 40 Vitellaria provenances from 10 African countries showed that the relative proportions of these compounds varied from region to region. Gallic acid was the major phenolic compound, comprising an average of 27% of the measured total phenols and exceeding 70% in some populations. Colorimetric analysis (101 samples) of total polyphenols extracted from shea butter into hexane gave an average of 97 ppm, with the values for different provenances varying between 62 and 135 ppm of total polyphenols.