Dynamic Pricing Without Knowing the Demand Function: Risk Bounds and Near-Optimal Algorithms

We consider a single-product revenue management problem where, given an initial inventory, the objective is to dynamically adjust prices over a finite sales horizon to maximize expected revenues. Realized demand is observed over time, but the underlying functional relationship between price and mean demand rate that governs these observations (otherwise known as the demand function or demand curve) is not known. We consider two instances of this problem: (i) a setting where the demand function is assumed to belong to a known parametric family with unknown parameter values; and (ii) a setting where the demand function is assumed to belong to a broad class of functions that need not admit any parametric representation. In each case we develop policies that learn the demand function “on the fly,” and optimize prices based on that. The performance of these algorithms is measured in terms of the regret: the revenue loss relative to the maximal revenues that can be extracted when the demand function is known prior to the start of the selling season. We derive lower bounds on the regret that hold for any admissible pricing policy, and then show that our proposed algorithms achieve a regret that is “close” to this lower bound. The magnitude of the regret can be interpreted as the economic value of prior knowledge on the demand function, manifested as the revenue loss due to model uncertainty

Petrology and Sedimentation of the Cambro-Ordovician Saq Sandstone, Saudi Arabia

The Saq Sandstone is 600m thick and of Cambro-Ordovician age (?). It is vertically and laterally uniform succession, >90% of which cross-stratified. It is a texturally and mineralogically mature, fine to coarse-grained quartz arenite, with subordinate shale, siltstone, breccia and conglomerate. The Saq Sandstone comprises an upward maturing and fining sequence. It was -largely derived from a craton interior made up of pre-existing and multi-cycle sedimentary rocks. A new formation (The Idwah Formation) overlying the Precambrian-Cambrian basement and older than the Saq Sandstone has been defined. This is a remnant of an earlier extensive cover over the peneplained Precambrian-Cambrian surface. The sandstone was partly or totally deposited in a tide-dominated shallow-shelf marine environment. Six Facies Associations have been recognized: (1) Facies Association A (Bar areas); (2) Facies Association B (Inter-Bar); (3) Facies Association C (Inner-shelf); (4) Facies Association D (Shoreline) and (5) Facies Association E (Scree). The Saq Sandstone was deposited intially during a transgression (Lower and Middle) and then during a regression (Upper) cycle. The regression producing a laterally extensive sheet of beach sandstone. The palaeocurrent pattern throughout Saq Sandstone is unidirectional (NE). This together with the orientation of the beach lamination, suggest that the source lay S to SW of the Saq Basin, although it is difficult to reconstruct a palaeoslope from tidally induced flows. The dominance of a single palaeoflow suggest a strongly asymmetrical tidal system

Sedimentation of Saq Sandstone, Central Saudi Arabia

The Cambro-Ordovician Saq Sandstone, over 600m thick, is a quartz-arenite and rests unconformably on the Arabian Shield from the Al-Qassim region in the South to the Jordan Border, Quartz generally comprises more than 95% of the sandstone and 91% of the quartz is monocrystalline quartz. Both chemistry and petrography studies indicate this Formation to be very mature sandstone. The Saq Sandstone is abundantly cross-stratified and contains marine fossils. It is considered to have formed on an open marine tidal shelf. The cross-strata are sometimes seen to form into major sand bars, and beach deposits occur within the sequence. The palaeoflow is unimodal, and is the result of asymmetrical tides operation on a sloping shelf. The palaeoflow, which is to the ME, is therefore seen as the main direction of sediment dispersal and is the direction in which the Cambrian sandstones in this whole area are replaced by mudstones. The Saq Sandstone was derived from a pre-existing sandstone since it contains detrital chert. In the process of becoming mature, there are probably many cycles of reworking before final deposition. There is some 50 Million years difference between the last recorded thermal event affecting the Arabian Shield and the deposition of this sandstone. This suggests that the development of a craton can occur in less than 50 Million years

The Israeli-Palestinian Water Distribution Revisited: Can Hydro-Entropy be a Useful Tool to Understand The Complexity of Hydropolitics?

Against the background of a failed Kerry peace initiative, severe militarization of the Gazaconflict in the summer of 2014 and an overall rise of tensions in the region and between superpowers, the question is posed if and how existing and new tools can help in fostering future waternegotiations between Palestine and Israel. We reflect on the narrative using a number of concepts.The Transboundary Waters Interaction NexuS (TWINS) which combines factors of cooperationand conflict and hydro-politics is applied to describe the interdependency of the political context,water governance and discourse in the case. In addition, we introduce the concept of hydroentropyand illustrate it for the Israel-Palestine case as part of the theories of water governanceand management. Hydro-entropy can be regarded as an information tool to indicate the levelof chaos and order of a water governance system and its natural counterpart, the water system.Hydro-entropy is described in four domains: physical-chemical, information systems, social sciencesand philosophy. By using insights from hydro-entropy, hydrolectics, hydro-psychology andsocio-hydrology, an approach such as TWINS can become even more illustrative and useful forthe parties involved in water negotiations. This positive effect is explained by the fact that theseconcepts and the TWINS-approach all draw on speech act theory

Redox Status Affects the Catalytic Activity of Glutamyl-tRNA Synthetase

Glutamyl-tRNA synthetases (GluRS) provide Glu-tRNA for different processes including protein synthesis, glutamine transamidation and tetrapyrrole biosynthesis. Many organisms contain multiple GluRSs, but whether these duplications solely broaden tRNA specificity or also play additional roles in tetrapyrrole biosynthesis is not known. Previous studies have shown that GluRS1, one of two GluRSs from the extremophile Acidithiobacillus ferrooxidans, is inactivated when intracellular heme is elevated suggesting a specific role for GluRS1 in the regulation of tetrapyrrole biosynthesis. We now show that, in vitro, GluRS1 activity is reversibly inactivated upon oxidation by hemin and hydrogen peroxide. The targets for oxidation-based inhibition were found to be cysteines from a SWIM zinc-binding motif located in the tRNA acceptor helix-binding domain. tRNAGlu was able to protect GluRS1 against oxidative inactivation by hemin plus hydrogen peroxide. The sensitivity to oxidation of A. ferrooxidans GluRS1 might provide a means to regulate tetrapyrrole and protein biosynthesis in response to extreme changes in both the redox and heme status of the cell via a single enzyme

Oxidative Stress Strongly Restricts the Effect of Codon Choice on the Efficiency of Protein Synthesis in \u3cem\u3eEscherichia coli\u3c/em\u3e

Introduction The response of enterobacteria to oxidative stress is usually considered to be regulated by transcription factors such as OxyR and SoxR. Nevertheless, several reports have shown that under oxidative stress the levels, modification and aminoacylation of tRNAs may be altered suggesting a role of codon bias in regulation of gene expression under this condition. Methods In order to characterize the effects of oxidative stress on translation elongation we constructed a library of 61 plasmids, each coding for the green fluorescent protein (GFP) translationally fused to a different set of four identical codons. Results Using these reporters, we observed that GFP production levels vary widely (~15 fold) when Escherichia coli K-12 is cultured in minimal media as a consequence of codon choice variations. When bacteria are cultured under oxidative stress caused by paraquat the levels of GFP produced by most clones is reduced and, in contrast to control conditions, the range of GFP levels is restricted to a ~2 fold range. Restricting elongation of particular sequences does not increase the range of GFP production under oxidative stress, but altering translation initiation rates leads to an increase in this range. Discussion Altogether, our results suggest that under normal conditions the speed of translation elongation is in the range of the speed of initiation and, consequently, codon choice impacts the speed of protein synthesis. In contrast, under oxidative stress translation initiation becomes much slower than elongation, limiting the speed of translation such that codon choice has at most only subtle effects on the overall output of translation

Oxidative stress strongly restricts the effect of codon choice on the efficiency of protein synthesis in Escherichia coli.

INTRODUCTION The response of enterobacteria to oxidative stress is usually considered to be regulated by transcription factors such as OxyR and SoxR. Nevertheless, several reports have shown that under oxidative stress the levels, modification and aminoacylation of tRNAs may be altered suggesting a role of codon bias in regulation of gene expression under this condition. METHODS In order to characterize the effects of oxidative stress on translation elongation we constructed a library of 61 plasmids, each coding for the green fluorescent protein (GFP) translationally fused to a different set of four identical codons. RESULTS Using these reporters, we observed that GFP production levels vary widely (~15 fold) when Escherichia coli K-12 is cultured in minimal media as a consequence of codon choice variations. When bacteria are cultured under oxidative stress caused by paraquat the levels of GFP produced by most clones is reduced and, in contrast to control conditions, the range of GFP levels is restricted to a ~2 fold range. Restricting elongation of particular sequences does not increase the range of GFP production under oxidative stress, but altering translation initiation rates leads to an increase in this range. DISCUSSION Altogether, our results suggest that under normal conditions the speed of translation elongation is in the range of the speed of initiation and, consequently, codon choice impacts the speed of protein synthesis. In contrast, under oxidative stress translation initiation becomes much slower than elongation, limiting the speed of translation such that codon choice has at most only subtle effects on the overall output of translation

International Perspective on the Persons Under the Burden of Debt

This study tackles loan repayments for debtors focused on Persons under the burden of debt. While financial facilitation, through lending funds and financial service providers, have contributed to supporting small projects especially for women who fall officially under the poverty line and in most need of financial capital, however, such debt instruments were provided with high interest rates. With absence of financial literacy and commercial investment experience, the borrowers are faced with imprisonment as part of the penal conditions in case of defaults in repayments or inability to repay the debtors. This study addresses the extent of applicability of such conditions on persons under the burden of debt and its relationship with financial support and economic empowermen