Market Definition and the Identification of Market Power in Monopolization Cases: A Critique and a Proposal

Although there is agreement on the basic economic principles that should apply to monopolization cases, there is no widely accepted paradigm for market definition or the identification of market power in such cases. This contrasts with the SSNIP paradigm of the DOJ-FTC Horizontal Merger Guidelines, which has gained wide acceptance in the two decades since its introduction. Moreover, misguided notions of market definition in monopolization cases still fall into a repeat commission of the “cellophane fallacy” of U.S. v. du Pont (1956). To correct this problem, we propose asking the following question in monopolization cases where exclusionary practices are alleged: Would preservation of the allegedly foreclosed competitor or group of competitors have led to a small but significant nontransitory decrease in price (SSNDP) by the defendant? This SSNDP test can help define the relevant market and, more importantly, can allow courts to focus directly on the anticompetitive effects of the defendant’s actions and thereby on the exercise of market power

Management of gangrenous sigmoid volvulus at Tenwek Hospital in western Kenya

Background: Bowel gangrene has a negative impact on outcomes of patients with sigmoid volvulus (SV). This study aimed at evaluating the management and outcomes of patients with gangrenous sigmoid volvulus and assessing the utility of primary anastomosis as a management option. Methods: An 11-year (January 2006-December 2016) descriptive retrospective chart review of patients managed for SV at Tenwek Hospital in Bomet, Kenya.Results: A total of 46 cases were identified, representing 25.4% of all cases of SV noted during the study period. The group had a mean age of 47.3 years (range 15-81), mean symptom duration of 2.2 days (range 2 hours-7 days) and a male predominance of 87%. Primary anastomosis (PA) without a proximal diverting colostomy was performed in 24 cases and a Hartmann's procedure (HP) was performed in 22 cases. Patients who had a HP were noted to have had a longer duration of symptoms and a higher incidence of peritonitis than those who had a PA (2.7 vs 1.8 days, P = 0.02; and 72% vs 42%, P = 0.04). All patients with concurrent colonic perforation (n = 3) had a HP. Seven patients died, giving an overall mortality of 15.2%. There was an anastomotic leak rate of 4.2% and a mortality rate of 8.3% among the subset of patients who had a PA.Conclusions: Primary anastomosis can be safely performed with good outcomes in patients with gangrenous SV, and the presence of bowel gangrene does not mandate a diverting colostomy. Keywords: sigmoid volvulus; bowel gangrene; primary anastomosis; colostomy; bowel obstructio

Extraordinarily high leaf selenium to sulfur ratios define ‘se-accumulator’ plants

Background and Aims: Selenium (Se) and sulfur (S) exhibit similar chemical properties. In flowering plants (angiosperms) selenate and sulfate are acquired and assimilated by common transport and metabolic pathways. It is hypothesized that most angiosperm species show little or no discrimination in the accumulation of Se and S in leaves when their roots are supplied a mixture of selenate and sulfate, but some, termed Se-accumulator plants, selectively accumulate Se in preference to S under these conditions. Methods: This paper surveys Se and S accumulation in leaves of 39 angiosperm species, chosen to represent the range of plant Se accumulation phenotypes, grown hydroponically under identical conditions. Results: The data show that, when supplied a mixture of selenate and sulfate: (1) plant species differ in both their leaf Se ([Se]leaf) and leaf S ([S]leaf) concentrations; (2) most angiosperms show little discrimination for the accumulation of Se and S in their leaves and, in non-accumulator plants, [Se]leaf and [S]leaf are highly correlated; (3) [Se]leaf in Se-accumulator plants is significantly greater than in other angiosperms, but [S]leaf, although high, is within the range expected for angiosperms in general; and (4) the Se/S quotient in leaves of Se-accumulator plants is significantly higher than in leaves of other angiosperms. Conclusion: The traits of extraordinarily high [Se]leaf and leaf Se/S quotients define the distinct elemental composition of Se-accumulator plants

Market Definition and the Identification of Market Power in Monopolization Cases: A Critique and a Proposal

Although there is agreement on the basic economic principles that should apply to monopolization cases, there is no widely accepted paradigm for market definition or the identification of market power in such cases. This contrasts with the SSNIP paradigm of the DOJ-FTC Horizontal Merger Guidelines, which has gained wide acceptance in the two decades since its introduction. Moreover, misguided notions of market definition in monopolization cases still fall into a repeat commission of the “cellophane fallacy” of U.S. v. du Pont (1956). To correct this problem, we propose asking the following question in monopolization cases where exclusionary practices are alleged: Would preservation of the allegedly foreclosed competitor or group of competitors have led to a small but significant nontransitory decrease in price (SSNDP) by the defendant? This SSNDP test can help define the relevant market and, more importantly, can allow courts to focus directly on the anticompetitive effects of the defendant’s actions and thereby on the exercise of market power

Dipole Interactions and Electrical Polarity in Nanosystems -- the Clausius-Mossotti and Related Models

Point polarizable molecules at fixed spatial positions have solvable electrostatic properties in classical approximation, the most familiar being the Clausius-Mossotti (CM) formula. This paper generalizes the model and imagines various applications to nanosystems. The behavior is worked out for a sequence of octahedral fragments of simple cubic crystals, and the crossover to the bulk CM law is found. Some relations to fixed moment systems are discussed and exploited. The one-dimensional dipole stack is introduced as an important model system. The energy of interaction of parallel stacks is worked out, and clarifies the diverse behavior found in different crystal structures. It also suggests patterns of self-organization which polar molecules in solution might adopt. A sum rule on the stack interaction is found and tested. Stability of polarized states under thermal fluctuations is discussed, using the one-dimensional domain wall as an example. Possible structures for polar hard ellipsoids are considered. An idea is formulated for enhancing polarity of nanosystems by intentionally adding metallic coatings.Comment: 18 pages (includes 6 embedded figures and 3 tables). New references, and other small improvements. Scheduled for publication by J. Chem. Phys., Jan. 200

Black Holes in Galaxy Mergers: Evolution of Quasars

Based on numerical simulations of gas-rich galaxy mergers, we discuss a model in which quasar activity is tied to the self-regulated growth of supermassive black holes in galaxies. Nuclear inflow of gas attending a galaxy collision triggers a starburst and feeds black hole growth, but for most of the duration of the starburst, the black hole is heavily obscured by surrounding gas and dust which limits the visibility of the quasar, especially at optical and UV wavelengths. Eventually, feedback energy from accretion heats the gas and expels it in a powerful wind, leaving a 'dead quasar'. Between buried and dead phases there is a window during which the galaxy would be seen as a luminous quasar. Because the black hole mass, radiative output, and distribution of obscuring gas and dust all evolve strongly with time, the duration of this phase of observable quasar activity depends on both the waveband and imposed luminosity threshold. We determine the observed and intrinsic lifetimes as a function of luminosity and frequency, and calculate observable lifetimes ~10 Myr for bright quasars in the optical B-band, in good agreement with empirical estimates and much smaller than the black hole growth timescales ~100 Myr, naturally producing a substantial population of 'buried' quasars. However, observed and intrinsic energy outputs converge in the IR and hard X-ray bands as attenuation becomes weaker and chances of observation greatly increase. We obtain the distribution of column densities along sightlines in which the quasar is seen above a given luminosity, and find that our result agrees remarkably well with observed estimates of the column density distribution from the SDSS for appropriate luminosity thresholds. (Abridged)Comment: 12 pages, 7 figures. Accepted for publication in ApJ (September 2005). Replacement with minor revisions from referee repor

Cityscapes without figures: geophysics, computing and the future of urban studies

Ye

Spin gap in the Quasi-One-Dimensional S=1/2 Antiferromagnet: Cu2(1,4-diazacycloheptane)2Cl4

Cu_{2}(1,4-diazacycloheptane)_{2}Cl_{4} contains double chains of spin 1/2 Cu^{2+} ions. We report ac susceptibility, specific heat, and inelastic neutron scattering measurements on this material. The magnetic susceptibility, $\chi(T)$, shows a rounded maximum at T = 8 K indicative of a low dimensional antiferromagnet with no zero field magnetic phase transition. We compare the $\chi(T)$ data to exact diagonalization results for various one dimensional spin Hamiltonians and find excellent agreement for a spin ladder with intra-rung coupling $J_1 = 1.143(3)$ meV and two mutually frustrating inter-rung interactions: $J_2 = 0.21(3)$ meV and $J_3 = 0.09(5)$ meV. The specific heat in zero field is exponentially activated with an activation energy $\Delta = 0.89(1)$ meV. A spin gap is also found through inelastic neutron scattering on powder samples which identify a band of magnetic excitations for $0.8 < \hbar\omega < 1.5$ meV. Using sum-rules we derive an expression for the dynamic spin correlation function associated with non-interacting propagating triplets in a spin ladder. The van-Hove singularities of such a model are not observed in our scattering data indicating that magnetic excitations in Cu_{2}(1,4-diazacycloheptane)_{2}Cl_{4} are more complicated. For magnetic fields above $H_{c1} \simeq 7.2$ T specific heat data versus temperature show anomalies indicating a phase transition to an ordered state below T = 1 K.Comment: 9 pages, 8 postscript figures, LaTeX, Submitted to PRB 8/4/97, e-mail Comments to [email protected]

Should multiple imputation be the method of choice for handling missing data in randomized trials?

The use of multiple imputation has increased markedly in recent years, and journal reviewers may expect to see multiple imputation used to handle missing data. However in randomized trials, where treatment group is always observed and independent of baseline covariates, other approaches may be preferable. Using data simulation we evaluated multiple imputation, performed both overall and separately by randomized group, across a range of commonly encountered scenarios. We considered both missing outcome and missing baseline data, with missing outcome data induced under missing at random mechanisms. Provided the analysis model was correctly specified, multiple imputation produced unbiased treatment effect estimates, but alternative unbiased approaches were often more efficient. When the analysis model overlooked an interaction effect involving randomized group, multiple imputation produced biased estimates of the average treatment effect when applied to missing outcome data, unless imputation was performed separately by randomized group. Based on these results, we conclude that multiple imputation should not be seen as the only acceptable way to handle missing data in randomized trials. In settings where multiple imputation is adopted, we recommend that imputation is carried out separately by randomized group.T Sullivan was supported by an Australian Postgraduate Award. I White was funded by the Medical Research Council (Unit Programme number U105260558). K Lee was supported by a National Health and Medical Research Council Career Development Fellowship (1053609)