The Formation and Evolution of Physician Treatment Styles: An Application to Cesarean Sections

Small-area-variation studies have shown that physician treatment styles differ substantially both between and within markets, controlling for patient characteristics. Using a data set containing the universe of deliveries in Florida over a 12-year period with consistent physician identifiers and a rich set of patient characteristics, we examine why treatment styles differ across obstetricians at a point in time, and why styles change over time. We find that the variation in c-section rates across physicians within a market is two to three times greater than the variation between markets. Surprisingly, residency programs explain less than four percent of the variation between physicians in their risk-adjusted c-section rates, even among newly-trained physicians. Although we find evidence that physicians, especially relatively inexperienced ones, learn from their peers, they do not substantially revise their prior beliefs regarding how patients should be treated due to the local exchange of information. Our results indicate that physicians are not likely to converge over time to a community standard; thus, within-market variation in treatment styles is likely to persist.

Wide spectrum attribution: Using deception for attribution intelligence in cyber attacks

Modern cyber attacks have evolved considerably. The skill level required to conduct a cyber attack is low. Computing power is cheap, targets are diverse and plentiful. Point-and-click crimeware kits are widely circulated in the underground economy, while source code for sophisticated malware such as Stuxnet is available for all to download and repurpose. Despite decades of research into defensive techniques, such as firewalls, intrusion detection systems, anti-virus, code auditing, etc, the quantity of successful cyber attacks continues to increase, as does the number of vulnerabilities identified. Measures to identify perpetrators, known as attribution, have existed for as long as there have been cyber attacks. The most actively researched technical attribution techniques involve the marking and logging of network packets. These techniques are performed by network devices along the packet journey, which most often requires modification of existing router hardware and/or software, or the inclusion of additional devices. These modifications require wide-scale infrastructure changes that are not only complex and costly, but invoke legal, ethical and governance issues. The usefulness of these techniques is also often questioned, as attack actors use multiple stepping stones, often innocent systems that have been compromised, to mask the true source. As such, this thesis identifies that no publicly known previous work has been deployed on a wide-scale basis in the Internet infrastructure. This research investigates the use of an often overlooked tool for attribution: cyber de- ception. The main contribution of this work is a significant advancement in the field of deception and honeypots as technical attribution techniques. Specifically, the design and implementation of two novel honeypot approaches; i) Deception Inside Credential Engine (DICE), that uses policy and honeytokens to identify adversaries returning from different origins and ii) Adaptive Honeynet Framework (AHFW), an introspection and adaptive honeynet framework that uses actor-dependent triggers to modify the honeynet envi- ronment, to engage the adversary, increasing the quantity and diversity of interactions. The two approaches are based on a systematic review of the technical attribution litera- ture that was used to derive a set of requirements for honeypots as technical attribution techniques. Both approaches lead the way for further research in this field

Mergers and Acquisitions in the Pharmaceutical and Biotech Industries

This paper examines the determinants of M&A activity in the pharmaceutical-biotechnology industry and the effects of mergers using propensity scores to control for merger endogeneity. Among large firms, we find that mergers are a response to excess capacity due to anticipated patent expirations and gaps in a company's product pipeline. For small firms, mergers are primarily an exit strategy for firms in financial trouble, as indicated by low Tobin's q, few marketed products, and low cash-sales ratios. We find that it is important to control for a firm's prior propensity to merge. Firms with relatively high propensity scores experienced slower growth of sales, employees and R&D regardless of whether they actually merged, which is consistent with mergers being a response to distress. Controlling for a firm's merger propensity, large firms that merged experienced similar changes in enterprise value, sales, employees, and R&D relative to similar firms that did not merge. Merged firms had slower growth in operating profit in the third year following a merger. Thus mergers may be a response to trouble, but they are not an effective solution for large firms. Neither mergers nor propensity scores have any effect on subsequent growth in enterprise value. This confirms that market valuations on average yield unbiased predictions of the effects of mergers. Small firms that merged experienced slower R&D growth relative to similar firms that did not merge, suggesting that post-merger integration may divert cash from R&D.

Three orbital model for the iron-based superconductors

The theoretical need to study the properties of the Fe-based high-T_c superconductors with reliable many-body techniques requires us to determine the minimum number of orbital degrees of freedom that will capture the physics of these materials. While the shape of the Fermi surface (FS) obtained with the local density approximation (LDA) can be reproduced by a two-orbital model, it has been argued that the bands that cross the chemical potential result from the strong hybridization of three of the Fe 3d orbitals. For this reason, a three-orbital Hamiltonian obtained with the Slater-Koster formalism by considering the hybridization of the As p orbitals with the Fe d_xz,d_yz, and d_xy orbitals is discussed here. This model reproduces qualitatively the FS shape and orbital composition obtained by LDA calculations for undoped pnictides when four electrons per Fe are considered. Within a mean-field approximation, its magnetic and orbital properties in the undoped case are described. With increasing Coulomb repulsion, four regimes are obtained: (1) paramagnetic, (2) magnetic (pi,0) spin order, (3) the same (pi,0) spin order but now including orbital order, and finally (4) a magnetic and orbital ordered insulator. The spin-singlet pairing operators allowed by the lattice and orbital symmetries are also constructed. It is found that for pairs of electrons involving up to diagonal nearest-neighbors sites, the only fully gapped and purely intraband spin-singlet pairing operator is given by Delta(k)=f(k)\sum_{alpha} d_{k,alpha,up}d_{-k,alpha,down} with f(k)=1 or f(k)=cos(k_x)cos(k_y) which would arise only if the electrons in all different orbitals couple with equal strength to the source of pairing

Iron Pnictides: Superconductivity in Multi-Orbital Systems

This work focuses on the development and implementation of microscopic models as well as their numerical and analytical study to elucidate the properties of the iron pnictides. There are many first principle and phenomenological studies of these materials, but there is a need for unbiased numerical calculations following an approach similar to the one used in the study of the Hubbard and t-J models for the cuprates. First a two orbital model for the pnictides, focusing on two hybridized Fe-d orbitals (dxz and dyz) is formulated, including hoppings between nearest and next nearest neighbors as well as on site Coulomb interactions. This model is studied numerically on a tilted 8-site cluster. The magnetic tendencies and the pairing operators allowed by lattice and orbital symmetries are calculated including a study of which of these operators are favored in the model. Next, Heisenberg terms, deduced from a strong coupling expansion, are added to enhance magnetic order found experimentally as well as to increase carrier attraction. Superconducting pairing symmetries are studied in both the hole and electron doped cases. In both cases, many pairing symmetries compete (A1g, B2g, B1g) in the physical parameter regime suggesting that small changes in parameters may render any of these three channels stable. In the hole doped case, ground states with pseudocrystal momentum k=(pi,pi) in the unfolded Brillouin zone are found. In the two Fe-atom unit cell, this indicates that the ground state involves anti-bonding, rather than bonding, combinations of the orbitals. The lowest state with k=(0,0) has only a slightly higher energy and may become the favored state in some regions of parameter space. To investigate the role that degeneracy, hybridization and nesting play in the origin of magnetic order in the pnictides we introduce a phenomenological two orbital model composed of non-hybridized bands. Using a variety of techniques, in the weak coupling regime it is shown that only the model with hybridized bands develops magnetic order while the other does not have local magnetization. However, both models display similar insulating magnetic order in the strong coupling limit. These results indicate that nesting is a necessary but not sufficient condition for the development of ordered states with local magnetization in multi-orbital Hubbard systems; the additional requirement is that the nested portions of the bands have the same orbital flavor. This condition can be achieved via strong hybridization of the orbitals in the weak coupling limit or via Fermi surface reconstruction induced by Coulomb interactions in the strong coupling regime. Finally, a three orbital model is developed which, in addition to the Fe 3-dxz and dyz orbitals, takes into account the Fe 3-dxy orbital, which is found to have weight in a small region around the Fermi surface in bandstructure calculations. Mean field calculations are performed guided by the results of the two orbital model. The proceeds of this work include the discovery of four distinct magnetic phases in the model as well as the tabulation of a variety of pairing operators and their single particle spectral functions to be compared with experimental observations. Good agreement is found between both models for the magnetic tendencies and pairing symmetries

Fit to be Tied: Social Network Structures and Evaluation Apprehension

In everyday life, people are typically connected to others, and these variably strong connections facilitate social influence related to a range of phenomena, from shaping body image and, impacting self-esteem to shaping behaviors through exhibiting social norms. Although the strongest ties (those most intimate and influential) can be very important to a person, there can also be a fear of judgement (i.e., evaluation apprehension) in those relationships. In online social networks, the relationship between tie strength and evaluation apprehension may emerge differently than in offline spaces due to affordances of social media, the asynchronous nature of computer-mediated communication, and the networked audience on social media; the potential influences of discrete ties may be additive because groups of strong ties may also exert a similar normative influence. In order to explore the possible links between evaluation apprehension and online social network structures (i.e., cumulative tie strength and network density), a study was conducted in which participants ( N = 96) first completed an initial online survey (assessing online evaluation apprehension and demographics), then viewed an in-lab visualization of their Twitter network (to capture social network structure characteristics), and finally completed a second survey (to capture network use habits). Analysis revealed associations between evaluation apprehension and tie strength as well as evaluation apprehension and network density with a moderate effect size. Results are interpreted to suggest that evaluation apprehension may be digitally contextual, predictors of tie strength may serve as affirmation, social network features may influence evaluation apprehension, and digital social networks may function as a conglomerate discipline-mechanism similar to that of the panopticon

On Dostoevsky’s Shoelaces and the Vicissitudes of Literary History

The article relates broadly to the English reception of Russian literature at the beginning of the twentieth century, and to the friendship between celebrated representatives of two generations of intermediaries and historians of Russian literature for the English, Maurice Baring and Dmitry Svyatopolk-Mirsky. More specifically it focuses on Baring’s recollection of an encounter in 1907 during which the young Mirsky allegedly expressed his passionate admiration for Dostoevsky and declared Tolstoy unworthy to untie Dostoevsky’s shoelaces. Baring’s own high regard for Dostoevsky had been manifest years before the Dostoevsky “craze” swept England in the teens of the century. Mirsky’s celebrity dates from the 1920s when, after Revolution and Civil War and aided by Baring, he lived in emigration in London, earning renown as author of arguably the finest history of Russian literature ever written for the English reader. However, Mirsky’s consistent opinion of Dostoevsky and his assessment of the relative eminence of Dostoevsky and Tolstoy in the writings of those years, far from cementing a bond with Baring, seem almost diametrically opposed to the latter’s recollection of their first encounter some 15 years before.  Nevertheless, traces of the lost Dostoevskyphile youth of Mirsky offer tentative vindication of Baring’s version. At the same time, though alien to the works by which Mirsky is best known, the exalted tenor of the surviving piece of juvenilia points obliquely ahead. It is macabrely suggestive of the expression of Mirsky’s growing Marxist and Leninist certainty from the late 1920s on, and of the faith or vision that in the 1930s took him back to the Soviet Union and his death

Constraints Imposed by Symmetry on Pairing Operators for the Pnictides

Considering model Hamiltonians that respect the symmetry properties of the pnictides, it is argued that pairing interactions that couple electrons at different orbitals with an orbital-dependent pairing strength inevitably lead to interband pairing matrix elements, at least in some regions of the Brillouin zone. Such interband pairing has not been considered of relevance in multiorbital systems in previous investigations. It is also observed that if, instead, a purely intraband pairing interaction is postulated, this requires that the pairing operator has the form $\Delta^+(k)=f(k) \sum_{\alpha} d^+_{k,\alpha,\uparrow}d^+_{-k, \alpha,\downarrow}$ where $\alpha$ labels the orbitals considered in the model and f(k) arises from the spatial location of the coupled electrons or holes. This means that the gaps at two different Fermi surfaces involving momenta $k_F$ and $k'_F$ can only differ by the ratio $f(k_F)/ f(k'_F)$ and that electrons in different orbitals must be subject to the same pairing attraction, thus requiring fine tuning. These results suggest that previously neglected interband pairing tendencies could actually be of relevance in a microscopic description of the pairing mechanism in the pnictides

Representing moisture fluxes and phase changes in glacier debris cover using a reservoir approach

Due to the complexity of treating moisture in supraglacial debris, surface energy balance models to date have neglected moisture infiltration and phase changes in the debris layer. The latent heat flux (QL) is also often excluded due to the uncertainty in determining the surface vapour pressure. To quantify the importance of moisture on the surface energy and climatic mass balance (CMB) of debris-covered glaciers, we developed a simple reservoir parameterization for the debris ice and water content, as well as an estimation of the latent heat flux. The parameterization was incorporated into a CMB model adapted for debris-covered glaciers. We present the results of two point simulations, using both our new “moist” and the conventional “dry” approaches, on the Miage Glacier, Italy, during summer 2008 and fall 2011. The former year coincides with available in situ glaciological and meteorological measurements, including the first eddy-covariance measurements of the turbulent fluxes over supraglacial debris, while the latter contains two refreeze events that permit evaluation of the influence of phase changes. The simulations demonstrate a clear influence of moisture on the glacier energy and mass-balance dynamics. When water and ice are considered, heat transmission to the underlying glacier ice is lower, as the effective thermal diffusivity of the saturated debris layers is reduced by increases in both the density and the specific heat capacity of the layers. In combination with surface heat extraction by QL, subdebris ice melt is reduced by 3.1% in 2008 and by 7.0% in 2011 when moisture effects are included. However, the influence of the parameterization on the total accumulated mass balance varies seasonally. In summer 2008, mass loss due to surface vapour fluxes more than compensates for the reduction in ice melt, such that the total ablation increases by 4.0 %. Conversely, in fall 2011, the modulation of basal debris temperature by debris ice results in a decrease in total ablation of 2.1 %. Although the parameterization is a simplified representation of the moist physics of glacier debris, it is a novel attempt at including moisture in a numerical model of debris-covered glaciers and one that opens up additional avenues for future research