Rounding Algorithms for a Geometric Embedding of Minimum Multiway Cut

The multiway-cut problem is, given a weighted graph and k >= 2 terminal nodes, to find a minimum-weight set of edges whose removal separates all the terminals. The problem is NP-hard, and even NP-hard to approximate within 1+delta for some small delta > 0. Calinescu, Karloff, and Rabani (1998) gave an algorithm with performance guarantee 3/2-1/k, based on a geometric relaxation of the problem. In this paper, we give improved randomized rounding schemes for their relaxation, yielding a 12/11-approximation algorithm for k=3 and a 1.3438-approximation algorithm in general. Our approach hinges on the observation that the problem of designing a randomized rounding scheme for a geometric relaxation is itself a linear programming problem. The paper explores computational solutions to this problem, and gives a proof that for a general class of geometric relaxations, there are always randomized rounding schemes that match the integrality gap.Comment: Conference version in ACM Symposium on Theory of Computing (1999). To appear in Mathematics of Operations Researc

The Independent Agency Myth

Republicans and Democrats are fighting the wrong fight over independent agencies. Republicans are wrong to see independent agencies as anathema to hierarchical presidential control of the administrative state. Democrats are likewise wrong to reflexively defend independent agency expertise and influence. Supreme Court Justices also need to break free from this trap; the ongoing struggle over independent agencies should be about facts, not partisan rhetoric. This Article seeks to reframe the fight over independent agencies. By surveying executive branch and independent agency department heads and supervisors during the Obama (2014) and Trump (2020) administrations, we have assembled unique and expansive data for evaluating agency performance. This data is also uniquely reliable: Notwithstanding fundamental differences in the rhetoric and strategies of these two administrations, these surveys of 554 political appointees and 4,776 career executives reinforce each other. The hallmarks of independent agency design (including staggered terms, for cause removal, and partisan balancing) neither facilitate nonpartisan expertise nor shield independent agencies from presidential control. Our findings are striking and disturbing. Contrary to the goals and assumptions of Progressive Era designers, independent agencies are not particularly expert, influential, or independent. Indeed, the very touchstones of today’s politics— party polarization and presidential unilateralism—cannot be squared with Progressive Era assumptions about both independent agency decision-making (including that agency decision-making is expert, apolitical, fact-based, and durable) and the willingness of political actors to support independent agency decision-making. Correspondingly, we recommend that Congress no longer turn to the independent agency design when establishing new federal programs. Our data also calls attention to a critical divide between major and smaller independents. In the maelstrom of party polarization and presidential efforts to gain control of major independent agencies, smaller independents are largely forgotten by a government that has too many agencies to manage and too many Senate-confirmed vacancies to fill. In other words, our government is overburdened and these agencies are its orphans. We recommend that smaller independents be relocated to the executive branch where they would benefit from coordinated executive branch initiatives, Department of Justice representation, and Office of Management and Budget review. For the major independent agencies, we argue that the independent agency design may not work well but ought not to be completely jettisoned. It is not obvious that these agencies will be more successful in the executive branch and there are risks of unintended negative consequences

Comparing Simulations and Observations of the Lyman-Alpha Forest I. Methodology

We describe techniques for comparing spectra extracted from cosmological simulations and observational data, using the same methodology to link Lyman-alpha properties derived from the simulations with properties derived from observational data. The eventual goal is to measure the coherence or clustering properties of Lyman-alpha absorbers using observations of quasar pairs and groups. We quantify the systematic underestimate in opacity that is inherent in the continuum fitting process of observed spectra over a range of resolution and signal-to-noise ratio. We present an automated process for detecting and selecting absorption features over the range of resolution and signal-to-noise of typical observational data on the Lyman-alpha "forest". Using these techniques, we detect coherence over transverse scales out to 500 h^{-1}_{50} kpc in spectra extracted from a cosmological simulation at z = 2.Comment: 52 pages, includes 14 figures, to appear in ApJ v566 Feb 200

Neutrino Oscillations as a Probe of Dark Energy

We consider a class of theories in which neutrino masses depend significantly on environment, as a result of interactions with the dark sector. Such theories of mass varying neutrinos (MaVaNs) were recently introduced to explain the origin of the cosmological dark energy density and why its magnitude is apparently coincidental with that of neutrino mass splittings. In this Letter we argue that in such theories neutrinos can exhibit different masses in matter and in vacuum, dramatically affecting neutrino oscillations. Both long and short baseline experiments are essential to test for these interactions. As an example of modifications to the standard picture, we consider simple models which may simultaneously account for the LSND anomaly, KamLAND, K2K and studies of solar and atmospheric neutrinos, while providing motivation to continue to search for neutrino oscillations in short baseline experiments such as BooNE.Comment: 5 pages, 1 figure, refs added, additional data considered, minor change in conclusions about LSN

Urinary diversion and bladder reconstruction/replacement using intestinal segments for intractable incontinence or following cystectomy

Background Surgery performed to improve or replace the function of the diseased urinary bladder has been carried out for over a century. Main reasons for improving or replacing the function of the urinary bladder are bladder cancer, neurogenic bladder dysfunction, detrusor overactivity and chronic inflammatory diseases of the bladder (such as interstitial cystitis, tuberculosis and schistosomiasis). There is still much uncertainty about the best surgical approach. Options available at the present time include: (1) conduit diversion (the creation of various intestinal conduits to the skin) or continent diversion (which includes either a rectal reservoir or continent cutaneous diversion), (2) bladder reconstruction and (3) replacement of the bladder with various intestinal segments. Objectives To determine the best way of improving or replacing the function of the lower urinary tract using intestinal segments when the bladder has to be removed or when it has been rendered useless or dangerous by disease. Search methods We searched the Cochrane Incontinence Group Specialised Trials Register (searched 28 October 2011), which contains trials identified from the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and CINAHL, and handsearching of journals and conference proceedings, and the reference lists of relevant articles. Selection criteria All randomised or quasi-randomised controlled trials of surgery involving transposition of an intestinal segment into the urinary tract. Data collection and analysis Trials were evaluated for appropriateness for inclusion and for risk of bias by the review authors. Three review authors were involved in the data extraction. Data were combined in a meta-analysis when appropriate. Main results Five trials met the inclusion criteria with a total of 355 participants. These trials addressed only five of the 14 comparisons pre-specified in the protocol. One trial reported no statistically significant differences in the incidence of upper urinary tract infection, uretero-intestinal stenosis and renal deterioration in the comparison of continent diversion with conduit diversion. The confidence intervals were all wide, however, and did not rule out important clinical differences. In a second trial, there was no reported difference in the incidence of upper urinary tract infection and uretero-intestinal stenosis when conduit diversions were fashioned from either ileum or colon. A meta-analysis of two trials showed no statistically significant difference in daytime or nocturnal incontinence amongst participants who were randomised to ileocolonic/ileocaecal segment bladder replacement compared to an ileal bladder replacement. However, one small trial suggested that bladder replacement using an ileal segment compared to using an ileocolonic segment may be better in terms of lower rates of nocturnal incontinence. There were no differences in the incidence of dilatation of upper tract, daytime urinary incontinence or wound infection using different intestinal segments for bladder replacement. However the data were reported for 'renal units', but not in a form that allowed appropriate patient-based paired analyses. No statistically significant difference was found in the incidence of renal scarring between anti-refluxing versus freely refluxing uretero-intestinal anastomotic techniques in conduit diversions and bladder replacement groups. Again, the outcome data were not reported as paired analysis or in form to carry out paired analysis. Authors' conclusions The evidence from the included trials was very limited. Only five studies met the inclusion criteria; these were small, of moderate or poor methodological quality, and reported few of the pre-selected outcome measures. This review did not find any evidence that bladder replacement (orthotopic or continent diversion) was better than conduit diversion following cystectomy for cancer. There was no evidence to suggest that bladder reconstruction was better than conduit diversion for benign disease. The clinical significance of data from one small trial suggesting that bladder replacement using an ileal segment compared to using an ileocolonic segment is better in terms of lower rates of nocturnal incontinence is uncertain. The small amount of usable evidence for this review suggests that collaborative multi centre studies should be organised, using random allocation where possible. This review is published as a Cochrane Review in the Cochrane Database of Systematic Reviews 2012, Issue 2. Cochrane Reviews are regularly updated as new evidence emerges and in response to comments and criticisms, and the Cochrane Database of Systematic Reviews should be consulted for the most recent version of the Review.</p

Differential C3NET reveals disease networks of direct physical interactions.

BACKGROUND: Genes might have different gene interactions in different cell conditions, which might be mapped into different networks. Differential analysis of gene networks allows spotting condition-specific interactions that, for instance, form disease networks if the conditions are a disease, such as cancer, and normal. This could potentially allow developing better and subtly targeted drugs to cure cancer. Differential network analysis with direct physical gene interactions needs to be explored in this endeavour. RESULTS: C3NET is a recently introduced information theory based gene network inference algorithm that infers direct physical gene interactions from expression data, which was shown to give consistently higher inference performances over various networks than its competitors. In this paper, we present, DC3net, an approach to employ C3NET in inferring disease networks. We apply DC3net on a synthetic and real prostate cancer datasets, which show promising results. With loose cutoffs, we predicted 18583 interactions from tumor and normal samples in total. Although there are no reference interactions databases for the specific conditions of our samples in the literature, we found verifications for 54 of our predicted direct physical interactions from only four of the biological interaction databases. As an example, we predicted that RAD50 with TRF2 have prostate cancer specific interaction that turned out to be having validation from the literature. It is known that RAD50 complex associates with TRF2 in the S phase of cell cycle, which suggests that this predicted interaction may promote telomere maintenance in tumor cells in order to allow tumor cells to divide indefinitely. Our enrichment analysis suggests that the identified tumor specific gene interactions may be potentially important in driving the growth in prostate cancer. Additionally, we found that the highest connected subnetwork of our predicted tumor specific network is enriched for all proliferation genes, which further suggests that the genes in this network may serve in the process of oncogenesis. CONCLUSIONS: Our approach reveals disease specific interactions. It may help to make experimental follow-up studies more cost and time efficient by prioritizing disease relevant parts of the global gene network.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Fish Assemblages and Benthic Biota Associated with Natural Hard-Bottom Areas in the Northwestern Gulf of Mexico

We report new observations of fish and benthic invertebrate assemblages at shallow-water (\u3c35 m depth), hard-bottom sites in the northwestern Gulf of Mexico. The biota of these previously unstudied areas and of three high-relief features in deeper water was observed during May 1980 using a combination of diver reconnaissance, videotape surveys, still-camera photography, and collection of invertebrates for identification. The six hard-bottom sites in shallow water typically comprised, small, often patchy, rock outcrops, and the associated sessile invertebrates included hydroids, bryozoans, sponges, octocorals, and ahermatypic stony corals. Sea urchins and arrow crabs were the most common motile epifauna. Fish assemblages were typified by red snapper, Atlantic spadefish, blue runner gray triggerfish, sheepshead, and tomtate. Three deeper stations had many of the same fish and invertebrate species, but also possessed a more tropical assemblage including fire corals, antipatharians, spiny lobsters, and a variety of tropical fish species. Hermatypic corals characteristic of some large, offshore banks were not abundant at any of the sites. Differences in the composition of fish assemblages between nearshore and deeper stations parallel those previously observed at petroleum platforms in the area. Shallow-water stations presumably experience a greater seasonal temperature range and lower absolute temperatures in winter and may be exposed to stresses such a lowered salinity and depleted oxygen levels due to their relative proximity to Mississippi River discharge. The fauna of these shallow hard-bottom sites has predominantly warm-temperate rather than tropical affinities

How states make their own air pollution somebody else’s problem

For now, one of the unfortunate byproducts of an industrial economy is air pollution, but states can often reap the benefits of industry and production while forcing other states to bear the costs. In a new study of tens of thousands of air polluters in the US, James E. Monogan III, David M. Konisky, and Neal D. Woods find that air polluters are more likely to be located near a downwind border compared to solid waste polluters; in effect, making air pollution another state’s problem