A general model of the public goods dilemma

An individually costly act that benefits all group members is a public good. Natural selection favors individual contribution to public goods only when some benefit to the individual offsets the cost of contribution. Problems of sex ratio, parasite virulence, microbial metabolism, punishment of noncooperators, and nearly all aspects of sociality have been analyzed as public goods shaped by kin and group selection. Here, I develop two general aspects of the public goods problem that have received relatively little attention. First, variation in individual resources favors selfish individuals to vary their allocation to public goods. Those individuals better endowed contribute their excess resources to public benefit, whereas those individuals with fewer resources contribute less to the public good. Thus, purely selfish behavior causes individuals to stratify into upper classes that contribute greatly to public benefit and social cohesion and to lower classes that contribute little to the public good. Second, if group success absolutely requires production of the public good, then the pressure favoring production is relatively high. By contrast, if group success depends weakly on the public good, then the pressure favoring production is relatively weak. Stated in this way, it is obvious that the role of baseline success is important. However, discussions of public goods problems sometimes fail to emphasize this point sufficiently. The models here suggest simple tests for the roles of resource variation and baseline success. Given the widespread importance of public goods, better models and tests would greatly deepen our understanding of many processes in biology and sociality

Real Rational Curves in Grassmannians

Fulton asked how many solutions to a problem of enumerative geometry can be real, when that problem is one of counting geometric figures of some kind having specified position with respect to some general fixed figures. For the problem of plane conics tangent to five general conics, the (surprising) answer is that all 3264 may be real. Similarly, given any problem of enumerating p-planes incident on some general fixed subspaces, there are real fixed subspaces such that each of the (finitely many) incident p-planes are real. We show that the problem of enumerating parameterized rational curves in a Grassmannian satisfying simple (codimension 1) conditions may have all of its solutions be real.Comment: 9 pages, 1 eps figure, uses epsf.sty. Below the LaTeX source is a MAPLE V.5 file which computes an example in the paper, and its outpu

Implementing Rapid Prototyping Using CNC Machining (CNC-RP) Through a CAD/CAM Interface

This paper presents the methodology and implementation of a rapid machining system using a CAD/CAM interface. Rapid Prototyping using CNC Machining (CNC-RP) is a method that has been developed which enables automatic generation of process plans for a machined component. The challenge with CNC-RP is not the technical problems of material removal, but with all of the required setup, fixture and toolpath planning, which has previously required a skilled machinist. Through the use of advanced geometric algorithms, we have implemented an interface with a CAD/CAM system that allows true automatic NC code generation directly from a CAD model with no human interaction; a capability necessary for a practical rapid prototyping system.Mechanical Engineerin

Neck pain and disability: A cross-sectional survey of the demographic and clinical characteristics of neck pain seen in a rheumatology clinic

This hospital-based cross-sectional cohort study examines the clinical and demographic features of neck pain, disability (using the Northwick Park neck pain questionnaire) and relationships to handicap in employment. Of 173 consecutive referrals to a rheumatology clinic with neck pain, 70% had neck/arm pain without neurological involvement, 13% other conditions, 11% nerve involvement and 5% other spinal pain. 141 patients (mean age 50 years) had mechanical or degenerative neck pain, of which 13% was probably work-related and 13% was trauma-related. 44 had taken sickness absence for an average of 30 weeks. Comorbidities were frequent (lumbar pain 51%). Those in work were significantly less disabled than those not working (p = 0.001) and those off sick (p < 0.01). Those reporting sleep disturbance, tearfulness and crying were significantly more disabled (p = 0.0001) than those who did not. Neck pain in secondary care is complicated by physical and emotional comorbidities. Comprehensive management requires a biopsychosocial model of care

Studies of Jet Quenching in HI Collisions at CMS

Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied using the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 inverse microbarn. Dijets were reconstructed using the CMS calorimeters, and a significant energy imbalance was observed between the leading jet and the away-side jet with increasing centrality. Correlation studies of jets and tracks reveal that the energy of the away-side jet is redistributed to lower pt and wider angle outside of the jet cone.Comment: 4 pages, 2 figures. Presented at XLVIth Rencontres de Moriond on QCD and High Energy Interaction, La Thuile, March 201

Leptoquark Production in e−e−e^-e^- Scattering

We consider the production of scalar and vector leptoquarks in $e^-e^-$ collisions. Although this reaction is not competitive with {\em e.g.} $e^-\gamma$ scattering for discovering these heavy states, it is the main process susceptible of differentiating two important classes of leptoquarks.Comment: 9 pages, talk presented at the Santa Cruz e-e- Workshop, UCSC, 4-5 September 199