Hodge theory and derived categories of cubic fourfolds

Cubic fourfolds behave in many ways like K3 surfaces. Certain cubics - conjecturally, the ones that are rational - have specific K3s associated to them geometrically. Hassett has studied cubics with K3s associated to them at the level of Hodge theory, and Kuznetsov has studied cubics with K3s associated to them at the level of derived categories. These two notions of having an associated K3 should coincide. We prove that they coincide generically: Hassett's cubics form a countable union of irreducible Noether-Lefschetz divisors in moduli space, and we show that Kuznetsov's cubics are a dense subset of these, forming a non-empty, Zariski open subset in each divisor.Comment: 37 pages. Applications to algebraic cycles added, and other improvements following referees' suggestions. This is a slightly expanded version of the paper to appear in Duke Math

A Rare Case of Reversible Encephalopathy Syndrome Accompanying Late Postpartum Eclampsia or Hypertensive Encephalopathy-A Clinical Dilemma

Posterior Reversible Encephalopathy Syndrome (PRES) refers to a clinic-radiologic diagnosis. Clinically it is characterized by non specific symptoms such as headache, confusion, visual disturbances and seizures. The radiological findings in PRES are thought to be due to vasogenic oedema, predominantly in the posterior cerebral hemispheres, and are reversible with appropriate management. We report a case of reversible encephalopathy diagnosed by MRI scan occurring in atypical areas like the caudate and lentiform nuclei of the brain following an uneventful lower segment caesarean section in a normotensive patient, who was successfully treated with antihypertensives, anticonvulsants and supportive treatment. The differential diagnosis of convulsions in the post-partum period is discussed

Contractibility and Asset Ownership: On-Board Computers and Governance in U.S. Trucking

We investigate how the contractibility of actions affecting the value of an asset affects asset ownership. We examine this by testing how on-board computer (OBC) adoption affects truck ownership. We develop and test the proposition that adoption should lead to less ownership by drivers, particularly for hauls where drivers have the greatest incentive to drive in non-optimal ways or engage in rent-seeking behavior. We find evidence in favor: OBC adoption leads to less driver ownership, especially for long hauls and hauls that use specialized trailers. We also find that non-owner drivers with OBCs drive better than those without them. These results suggest that technology-enabled increases in contractibility may lead to less independent contracting and larger firms.

Make Versus Buy in Trucking: Asset Ownership, Job Design and Information

Explaining patterns of asset ownership in the economy is a central goal of both organizational economics and industrial organization. We develop a model of asset ownership in trucking, which we test by examining how the adoption of different classes of on-board computers (OBCs) between 1987 and 1997 influenced whether shippers use their own trucks for hauls or contract with for-hire carriers. We find that OBCs' incentive-improving features pushed hauls toward private carriage, but their resource-allocation-improving features pushed them toward for-hire carriage. We conclude that ownership patterns in trucking reflect the importance of both incomplete contracts (Grossman and Hart (1986)) and of job design and measurement issues (Holmstrom and Milgrom (1994)).

A sketch planning methodology for determining interventions for bicycle and pedestrian crashes: an ecological approach

Bicycle and pedestrian safety planning have recently been gaining increased attention. With this focus, however, comes increased responsibilities for planning agencies and organizations tasked with evaluating and selecting safety interventions, a potentially arduous task given limited staff and resources. This study presents a sketch planning framework based on ecological factors that attempts to provide an efficient and effective method of selecting appropriate intervention measures. A Chicago case study is used to demonstrate how such a method may be applied

Total plankton respiration in the Chesapeake Bay plume

Total plankton respiration (TPR) was measured at 17 stations within the Chesapeake Bay plume off the Virginia coast during March, June, and October 1980. Elevated rates of TPR, as well as higher concentrations of chlorophyll a and phaeopigment a, were found to be associated with the Bay plume during each survey. The TPR rates within the Bay plume were close to those found associated with the Hudson River plume for comparable times of the year. The data examined indicate that the Chesapeake Bay plume stimulates biological activity and is a source of organic loading to the contiguous shelf ecosystem

Update on tests of the Cen A neutron-emission model of highest energy cosmic rays

We propose that neutron emission from Cen A dominates the cosmic ray sky at the high end of the spectrum. Neutrons that are able to decay generate proton diffusion fronts, whereas those that survive decay produce a spike in the direction of the source. We use recent data reported by the Pierre Auger Collaboration to normalize the injection spectrum and estimate the required luminosity in cosmic rays. We find that such a luminosity, L_{CR} ~ 5 x 10^{40} erg/s, is considerably smaller than the bolometric luminosity of Cen A, L_{bol} ~ 10^{43} erg/s. We compute the incoming current flux density as viewed by an observer on Earth and show that the anisotropy amplitude is in agreement with data at the 1\sigma level. Regardless of the underlying source model, our results indicate that after a decade of data taking the Pierre Auger Observatory will be able to test our proposal.Comment: To be published in PR

Range-resolved signal processing for fibre segment interferometry applied to dynamic long-gauge length strain sensing

A range-resolved interferometric signal processing technique using sinusoidal optical frequency modulation is applied to fibre segment interferometry. Here, six optical fibre segments of gauge length 12.5 cm are used as interferometric strain sensors and are formed between seven weak, broadband fibre Bragg gratings, acting as in-fibre partial reflectors. In a very simple and cost-effective optical setup using injection current modulation of a laser diode source, interferometric measurement of acoustic wave propagation in a metal rod is used to demonstrate the capabilities of the technique