Non-stationary Stochastic Optimization

We consider a non-stationary variant of a sequential stochastic optimization problem, in which the underlying cost functions may change along the horizon. We propose a measure, termed variation budget, that controls the extent of said change, and study how restrictions on this budget impact achievable performance. We identify sharp conditions under which it is possible to achieve long-run-average optimality and more refined performance measures such as rate optimality that fully characterize the complexity of such problems. In doing so, we also establish a strong connection between two rather disparate strands of literature: adversarial online convex optimization; and the more traditional stochastic approximation paradigm (couched in a non-stationary setting). This connection is the key to deriving well performing policies in the latter, by leveraging structure of optimal policies in the former. Finally, tight bounds on the minimax regret allow us to quantify the "price of non-stationarity," which mathematically captures the added complexity embedded in a temporally changing environment versus a stationary one

How high frequency trading affects a market index

The relationship between a market index and its constituent stocks is complicated. While an index is a weighted average of its constituent stocks, when the investigated time scale is one day or longer the index has been found to have a stronger effect on the stocks than vice versa. We explore how this interaction changes in short time scales using high frequency data. Using a correlation-based analysis approach, we find that in short time scales stocks have a stronger influence on the index. These findings have implications for high frequency trading and suggest that the price of an index should be published on shorter time scales, as close as possible to those of the actual transaction time scale.We would like to thank Yoash Shapira, Idan Michaeli and Dustin Plotnick for all of their help. DYK and EBJ acknowledge support in part by the Tauber Family Foundation and the Maguy-Glass Chair in Physics of Complex Systems at Tel Aviv University. HES and DYK thank the support of the Office of Naval Research (ONR, Grant N00014-09-1-0380, Grant N00014-12-1-0548), Keck Foundation and the NSF (Grant CMMI 1125290) for support. This work was also supported by the Intelligence Advanced Research Projects Activity (IARPA) via Department of Interior National Business Center (DoI/NBC) contract number D12PC00285. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright annotation thereon. Disclaimer: The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of IARPA, DoI/NBC, or the U.S. Government. (Tauber Family Foundation; Maguy-Glass Chair in Physics of Complex Systems at Tel Aviv University; N00014-09-1-0380 - Office of Naval Research (ONR); N00014-12-1-0548 - Office of Naval Research (ONR); Keck Foundation; CMMI 1125290 - NSF; D12PC00285 - Intelligence Advanced Research Projects Activity (IARPA) via Department of Interior National Business Center (DoI/NBC))Published versio

Moždana vazomotorna reaktivnost i okluzivna bolest karotidnih arterija

Cerebral autoregulation is a mechanism that enables relatively constant cerebral blood flow during variations of cerebral perfusion pressure. The differences between cerebral blood flow at rest and after administration of a potent vasodilatory stimulus test such as hypercapnia reflect cerebral vasomotor reactivity defined as the vasodilation capacity of cerebral arterioles to external stimuli, providing important information about the cerebral hemodynamic status. Cerebral vasomotor reactivity provides important information about the cerebral hemodynamic status. In this article, cerebral vasomotor reactivity assessment tests are presented, with emphasis on transcranial Doppler, as well as the use of transcranial Doppler in assessing cerebral vasomotor reactivity in carotid stenosis, occlusion, and the importance of cerebral vasomotor reactivity for carotid surgery.Moždana autoregulacija je mehanizam koji omogućava relativno ustaljeni moždani protok krvi za vrijeme promjena tlaka prokrvljenosti mozga. Razlike između moždanog protoka krvi u mirovanju i nakon testa snažne vazodilatacijske stimulacije poput hiperkapnije odražavaju moždanu vazomotornu reaktivnost definiranu kao vazodilatacijski kapacitet moždanih arteriola za vanjske poticaje, pružajući važne podatke o moždanom hemodinamskom statusu. Moždana vazomotorna reaktivnost daje važne informacije o statusu moždane hemodinamike. U članku se prikazuju testovi za procjenu moždane vazomotorne reaktivnosti s naglaskom na transkranijski Doppler, te primjena transkranijskog Dopplera u procjeni moždane vazomotorne reaktivnosti kod karotidne stenoze, okluzije, kao i važnost moždane vazomotorne reaktivnosti za kirurgiju karotidnih arterija

Dynamics of Stock Market Correlations

We present a novel approach to the study the dynamics of stock market correlations. This is achieved through an innovative visualization tool that allows an investigation of the structure and dynamics of the market, through the study of correlations. This is based on the Stock Market Holography (SMH) method recently introduced. This qualitative measure is complemented by the use of the eigenvalue entropy measure, to quantify how the information in the market changes in time. Using this innovative approach, we analyzed data from the New York Stock Exchange (NYSE), and the Tel Aviv Stock Exchange (TASE), for daily trading data for the time period of 2000–2009. This paper covers these new concepts for the study of financial markets in terms of structure and information as reflected by the changes in correlations over time.Correlation, Stock Market Holography, eigenvalue entropy, sliding window

Duretovo krvarenje: rijetka komplikacija ishemijskog moždanog udara u području središnje moždane arterije - Prikaz slučaja

We report on an unusual case of brainstem Duret hemorrhage after ischemic stroke in the anterior circulation. The patient showed a clinical and neuroradiological picture of an acute and malignant middle cerebral artery infarct with increased intracranial pressure followed by a brainstem hemorrhage. The report suggests that the descending transtentorial herniation of any etiology might be complicated by a Duret hemorrhage.Opisuje se rijedak slučaj Duretova krvarenja moždanoga debla nakon ishemijskog moždanog udara u prednjem krvotoku. Bolesnik je pokazivao kliničku i neuroradiološku sliku akutnog i zloćudnog infarkta središnje moždane arterije uz povišen intrakranijski tlak, nakon čega je uslijedilo krvarenje u moždanom deblu. Ovaj prikaz ukazuje na to da se Duretovo krvarenje može pojaviti kao komplikacija kod silazne transtentorijske hernijacije bilo koje etiologije

Renormalization group approach to vibrational energy transfer in protein

Renormalization group method is applied to the study of vibrational energy transfer in protein molecule. An effective Lagrangian and associated equations of motion to describe the resonant energy transfer are analyzed in terms of the first-order perturbative renormalization group theory that has been developed as a unified tool for global asymptotic analysis. After the elimination of singular terms associated with the Fermi resonance, amplitude equations to describe the slow dynamics of vibrational energy transfer are derived, which recover the result obtained by a technique developed in nonlinear optics [S.J. Lade, Y.S. Kivshar, Phys. Lett. A 372 (2008) 1077].Comment: 11 page

Deciphering M-T diagram of shape memory Heusler alloys: reentrance, plateau and beyond

We present our recent results on temperature behaviour of magnetization observed in Ni_47Mn_39In_14 Heusler alloys. Three regions can be distinguished in the M-T diagram: (I) low temperature martensitic phase (with the Curie temperature T_CM = 140 K), (II) intermediate mixed phase (with the critical temperature T_MS = 230 K) exhibiting a reentrant like behavior (between T_CM and T_MS) and (III) high temperature austenitic phase (with the Curie temperature T_CA = 320 K) exhibiting a rather wide plateau region (between T_MS and T_CA). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entire M-T diagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg-Landau scenario

Impact of emphysema heterogeneity on pulmonary function

Results: The majority (128/160) of the subjects with COPD had a heterogeneity greater than zero. After adjusting for age, gender, smoking history, and extent of emphysema, heterogeneity in depicted disease in upper lobe dominant cases was positively associated with pulmonary function measures, such as FEV1 Predicted (p<.001) and FEV1/FVC (p<.001), as well as disease severity (p<0.05). We found a negative association between HI% , RV/TLC (p<0.001), and DLco% (albeit not a statistically significant one, p = 0.06) in this group of patients

Yield quantitative trait loci from wild tomato are predominately expressed by the shoot

Plant yield is the integrated outcome of processes taking place above and below ground. To explore genetic, environmental and developmental aspects of fruit yield in tomato, we phenotyped an introgression line (IL) population derived from a cross between the cultivated tomato (Solanum lycopersicum) and a wild species (Solanum pennellii). Both homozygous and heterozygous ILs were grown in irrigated and non-irrigated fields and evaluated for six yield components. Thirteen lines displayed transgressive segregation that increased agronomic yield consistently over 2 years and defined at least 11 independent yield-improving QTL. To determine if these QTL were expressed in the shoots or the roots of the plants, we conducted field trials of reciprocally grafted ILs; out of 13 lines with an effect on yield, 10 QTL were active in the shoot and only IL8-3 showed a consistent root effect. To further examine this unusual case, we evaluated the metabolic profiles of fruits from both the homo- and heterozygous lines for IL8-3 and compared these to those obtained from the fruit of their equivalent genotypes in the root effect population. We observed that several of these metabolic QTL, like the yield QTL, were root determined; however, further studies will be required to delineate the exact mechanism mediating this effect in this specific line. The results presented here suggest that genetic variation for root traits, in comparison to that present in the shoot, represents only a minor component in the determination of tomato fruit yield