Ricci Collineations of the Bianchi Types I and III, and Kantowski-Sachs Spacetimes

Ricci collineations of the Bianchi types I and III, and Kantowski-Sachs space- times are classified according to their Ricci collineation vector (RCV) field of the form (i)-(iv) one component of $\xi^a (x^b)$ is nonzero, (v)-(x) two components of $\xi^a (x^b)$ are nonzero, and (xi)-(xiv) three components of $\xi^a (x^b)$ are nonzero. Their relation with isometries of the space-times is established. In case (v), when $det(R_{ab}) = 0$, some metrics are found under the time transformation, in which some of these metrics are known, and the other ones new. Finally, the family of contracted Ricci collineations (CRC) are presented.Comment: 21 Pages, LaTeX, no figures, accepted for publication in the International Journal of Modern Physics

Refractive Index Enhancement with Vanishing Absorption in an Atomic Vapor

We report a proof-of-principle experiment where the refractive index of an atomic vapor is enhanced while maintaining vanishing absorption of the beam. The key idea is to drive alkali atoms in a vapor with appropriate control lasers and induce a gain resonance and an absorption resonance for a probe beam in a two-photon Raman configuration. The strength and the position of these two resonances can be manipulated by changing the parameters of the control lasers. By using the interference between these two resonances, we obtain an enhanced refractive index without an increase in the absorption.Comment: 11 pages, 4 figure

Design Chart for Reinforced Concrete Rectangular Section

Design charts are very useful for fast determining the percentage of reinforcement for singly and doubly reinforced concrete beams having known cross-sectional dimensions, characteristic strengths of the concrete and steel, and the ultimate design moment. A complete set of design charts is given in BS: 8110 - 85: Part 3, but it seems difficult to use these charts especially for doubly reinforced beams. In this paper, a straight-forward design chart has been developed based on BS: 8110 – 97 design rules. Several design examples have been solved using the developed chart and good results have been obtained

Being Modern in the Nurcu Way

One of the defining conflicts of modern Turkish life is the great tension between society and the state. This tension has been articulated in terms of the conflict between Islamic social movements and the state ideology, Kemalism. Alberto Melucci argues that social movements constitute an active resistance that seeks to free everyday life from colonization by central government so that individuals may realize their unique potential and assert their collective identity. This aptly describes the Nurcu movement, an Islamic faith movement based on the writings of Said Nursi (1876-1960). Nursi suffered persecution at the hands of the Kemalist elite and was eventually exiled. Even his dead body posed a 'security threat'. After his death, his body was exhumed by military coup leaders in 1960 and reburied at an unknown location

Cost Benefit Analysis Of The Structures Designed For Alternative Seismic Hazard Levels

In this study, multiple performance objectives under the various earthquake hazard levels are investigated. In case of well defined earthquake hazard, as an alternative of classical earthquake resistant design principles, it is possible to design structures at different performances depending on structure's initial cost and economic life. In this study, costs of the structure with different performance levels are discussed.Current study is carried out on the reinforced concrete structures that are designed and analyzed for various seismic hazard levels. The aim is to determine, if the risk is released, whether the economic losses can be acceptable or not. In the study, cost of reinforced concrete ductile frames and dual systems that are designed for various seismic performances, are also compared for the economical aspects.To that end, in the first step 3, 5 and 8 storey frames and dual systems of several structures at Life Safety and Immediate Occupancy performance levels was designed for the earthquake hazards of 2% and 10% probability of exceedance in 50 years. The study reveals that if both direct and indirect effects of earthquake such as retrofitting costs, cost of temporary moving, temporary accommodation costs, cost of demolition and reconstructing the building, cost of damage to household goods and business disruption, social disturbance, are be taken into consideration, initial design performance level can be accepted as Immediate Occupancy performance level rather than Life Safety performance which is proposed current earthquake codes. The cost due to injuries and cost due to loss of lives are not included

Circuit lengths of graphs for the Picard group

In this paper, we examine some properties of suborbital graphs for the Picard group. We obtain edge and circuit conditions, then propose a conjecture for the graph to be forest. This paper is an extension of some results in (Jones et al. in The Modular Group and Generalized Farey Graphs, pp. 316-338, 1991)

Structural dynamics and transient lipid binding of synaptobrevin-2 tune SNARE assembly and membrane fusion.

Intrinsically disordered proteins (IDPs) and their conformational transitions play an important role in neurotransmitter release at the neuronal synapse. Here, the SNARE proteins are essential by forming the SNARE complex that drives vesicular membrane fusion. While it is widely accepted that the SNARE proteins are intrinsically disordered in their monomeric prefusion form, important mechanistic aspects of this prefusion conformation and its lipid interactions, before forming the SNARE complex, are not fully understood at the molecular level and remain controversial. Here, by a combination of NMR and fluorescence spectroscopy methods, we find that vesicular synaptobrevin-2 (syb-2) in its monomeric prefusion conformation shows high flexibility, characteristic for an IDP, but also a high dynamic range and increasing rigidity from the N to C terminus. The gradual increase in rigidity correlates with an increase in lipid binding affinity from the N to C terminus. It could also explain the increased rate for C-terminal SNARE zippering, known to be faster than N-terminal SNARE zippering. Also, the syb-2 SNARE motif and, in particular, the linker domain show transient and weak membrane binding, characterized by a high off-rate and low (millimolar) affinity. The transient membrane binding of syb-2 may compensate for the repulsive forces between the two membranes and/or the SNARE motifs and the membranes, helping to destabilize the hydrophilic-hydrophobic boundary in the bilayer. Therefore, we propose that optimum flexibility and membrane binding of syb-2 regulate SNARE assembly and minimize repulsive forces during membrane fusion

An analysis of order review

Ankara : Department of Industrial Engineering and the Institute of Engineering and Sciences of Bilkent Univ., 1995.Thesis (Master's) -- Bilkent University, 1995.Includes bibliographical references.Order Review/Release (ORR) activities have mostly been ignored in past job shop research. In the majority of these studies, arriving jobs are immediately released to the shop floor without considering any information about the job and the system status. In practice, however, jobs arriving at the shop are first collected in a pool and then released periodically according to some release criterion. Although practitioners use ORR mechanisms to improve shop floor performance, researchers have found limited supports for the use of these input regulation policies. In this thesis, we reexamine the problem in a capacitated system. Specifically, we compare the performances of the ORR policies in a job shop with finite buffer capacities and material handling considerations. A new ORR mechanism is also proposed and compared with other methods.Karapınar, H YavuzM.S