New interactions in the dark sector mediated by dark energy

Cosmological observations have revealed the existence of a dark matter sector, which is commonly assumed to be made up of one particle species only. However, this sector might be more complicated than we currently believe: there might be more than one dark matter species (for example, two components of cold dark matter or a mixture of hot and cold dark matter) and there may be new interactions between these particles. In this paper we study the possibility of multiple dark matter species and interactions mediated by a dark energy field. We study both the background and the perturbation evolution in these scenarios. We find that the background evolution of a system of multiple dark matter particles (with constant couplings) mimics a single fluid with a time-varying coupling parameter. However, this is no longer true on the perturbative level. We study the case of attractive and repulsive forces as well as a mixture of cold and hot dark matter particles

Slow roll inflation in the presence of a dark energy coupling

In models of coupled dark energy, in which a dark energy scalar field couples to other matter components, it is natural to expect a coupling to the inflaton as well. We explore the consequences of such a coupling in the context of single-field slow-roll inflation. Assuming an exponential potential for the quintessence field we show that the coupling to the inflaton causes the quintessence field to be attracted toward the minimum of the effective potential. If the coupling is large enough, the field is heavy and is located at the minimum. We show how this affects the expansion rate and the slow-roll of the inflaton field, and therefore the primordial perturbations generated during inflation. We further show that the coupling has an important impact on the processes of reheating and preheating

The Effect of Textual Errors on Dyadic and Individual Learning

The Major Objective of the Present Experiment Was to Assess the Effects of Textual Errors on Dyadic and Individual Learning. One Hundred Undergraduates Were Taught a Four-Step Learning Strategy, after Which They Studied a Text Passage Either Dyadically or Individually. Half of the Passages within Both Conditions Contained Syntactic Errors. Total Recall Measures Indicated that Dyads Performed Better Than Individuals on Recall of Text in Sections Not Containing Errors, Whereas the Groups Did Not Differ on Recall of the Material in Text Sections Containing Errors. Further, Dyads Outscored Individuals on Measures of Recall of Error Location, Error Frequency, and Perceived Difficulty of the Text Sections Which Contained Errors. in Addition, Subjective Processing Measures Indicated that Motivation and Interest Were Strongly Related to Recall. © 1989, SAGE Publications. All Rights Reserved

Cosmological Constraints on Dissipative Models of Inflation

(Abridged) We study dissipative inflation in the regime where the dissipative term takes a specific form, \Gamma=\Gamma(\phi), analyzing two models in the weak and strong dissipative regimes with a SUSY breaking potential. After developing intuition about the predictions from these models through analytic approximations, we compute the predicted cosmological observables through full numerical evolution of the equations of motion, relating the mass scale and scale of dissipation to the characteristic amplitude and shape of the primordial power spectrum. We then use Markov Chain Monte Carlo techniques to constrain a subset of the models with cosmological data from the cosmic microwave background (WMAP three-year data) and large scale structure (SDSS Luminous Red Galaxy power spectrum). We find that the posterior distributions of the dissipative parameters are highly non-Gaussian and their allowed ranges agree well with the expectations obtained using analytic approximations. In the weak regime, only the mass scale is tightly constrained; conversely, in the strong regime, only the dissipative coefficient is tightly constrained. A lower limit is seen on the inflation scale: a sub-Planckian inflaton is disfavoured by the data. In both weak and strong regimes, we reconstruct the limits on the primordial power spectrum and show that these models prefer a {\it red} spectrum, with no significant running of the index. We calculate the reheat temperature and show that the gravitino problem can be overcome with large dissipation, which in turn leads to large levels of non-Gaussianity: if dissipative inflation is to evade the gravitino problem, the predicted level of non-Gaussianity might be seen by the Planck satellite.Comment: 14 pages, 9 figures, Accepted by JCAP without text changes, References adde

Standard Cosmological Evolution in a Wide Range of f(R) Models

Using techniques from singular perturbation theory, we explicitly calculate the cosmological evolution in a class of modified gravity models. By considering the (m)CDTT model, which aims to explain the current acceleration of the universe with a modification of gravity, we show that Einstein evolution can be recovered for most of cosmic history in at least one f(R) model. We show that a standard epoch of matter domination can be obtained in the mCDTT model, providing a sufficiently long epoch to satisfy observations. We note that the additional inverse term will not significantly alter standard evolution until today and that the solution lies well within present constraints from Big Bang Nucleosynthesis. For the CDTT model, we analyse the ``recent radiation epoch'' behaviour (a \propto t^{1/2}) found by previous authors. We finally generalise our findings to the class of inverse power-law models. Even in this class of models, we expect a standard cosmological evolution, with a sufficient matter domination era, although the sign of the additional term is crucial.Comment: 15 pages, 6 figures (1 new figure), new version considers both CDTT and mCDTT models. References added. Accepted by Phys Rev

Meningococcal Disease in Patients With Human Immunodeficiency Virus Infection: A Review of Cases Reported Through Active Surveillance in the United States, 2000-2008.

BackgroundAlthough human immunodeficiency virus (HIV) infection is an established risk factor for several bacterial infections, the association between HIV infection and meningococcal disease remains unclear.MethodsExpanded chart reviews were completed on persons with meningococcal disease and HIV infection reported from 2000 through 2008 from 9 US sites participating in an active population-based surveillance system for meningococcal disease. The incidence of meningococcal disease among patients meeting Centers for Disease Control and Prevention acquired immune deficiency syndrome (AIDS) surveillance criteria was estimated using data from the National HIV Surveillance System for the participating sites.ResultsThirty-three cases of meningococcal disease in individuals with HIV infection were reported from participating sites, representing 2.0% of all reported meningococcal disease cases. Most (75.8%) persons with HIV infection were adult males aged 25 to 64 years old. Among all meningococcal disease cases aged 25 to 64 years old, case fatality ratios were similar among HIV-infected and HIV-uninfected persons (13.3% vs 10.6%; P = .6). The cumulative, mean incidence of meningococcal disease among patients aged 25 to 64 years old with HIV infection ever classified as AIDS was 3.5 cases per 100000 person years (95% confidence interval [CI], 2.1-5.6), compared with 0.3 cases per 100000 person years (95% CI, 0.3-0.3) for persons of the same age group not reported to have AIDS (relative risk = 12.9; 95% CI, 7.9-20.9).ConclusionsIndividuals with HIV infection meeting the AIDS surveillance case definition have a higher incidence of meningococcal disease compared with the general adult population

Truck Route Access Evaluation: Paducah-McCraken County, US 60 Business Route and Locust Drive, Site #14

There are two main objectives of the Freight Movement and Intermodal Access in Kentucky Study (SPR 98-189) undertaken by the Kentucky Transportation Center for the Kentucky Transportation Cabinet: evaluation of the access for trucks between intermodal or other truck generating sites and the National Highway System (NHS); and furthering the understanding of freight commodity flows throughout the state. This report summarizes the access evaluation for one cluster of facilities located in McCracken county in the Purchase Area Development District (ADD) and KYTC Highway District # 1. The location of the site in Paducah is shown in Figure 1. Work on other specific sites as well as the freight commodity flow task are on-going and are documented elsewhere

Promoting Functional Literacy through Cooperative Learning

The Effects of Cooperative Learning Strategy Manipulations on the Enactment and Recall of a Medical Procedure Were Explored. One Hundred and Twenty-Three College Students Completed the Experiment. during Training, Participants Were Randomly Assigned to a Dyad in One of Four Conditions: (A) No-Strategy, (B) Baseline Strategy, (C) Prompting Strategy, and (D) Planning Strategy. during Testing, Participants Both Performed and Produced Written Recalls of the Procedure Instructions. Test Order Was Counterbalanced within Dyad. Training and Test Performances Were Videotaped. the Planning Group Produced the Best Recalls and Recalled More Conditions of the Procedure. the Prompting Group Performed Best. Recall of the Procedure in All Groups Was Enhanced by Prior Performance. However, Performance Was Enhanced by Prior Recall in Only Two Groups. the Groups Differed Also in the Nature of the Transition from Training to Testing. Theoretical and Applied Implications of These Findings Are Discussed. © 1988, SAGE Publications. All Rights Reserved