2,665 research outputs found
Do-or-die life cycles and diverse post-infection resistance mechanisms limit the evolution of parasite host ranges
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.In light of the dynamic nature of parasite host ranges and documented potential for rapid host shifts, the observed high host specificity of most parasites remains an ecological paradox. Different variants of host-use trade-offs have become a mainstay of theoretical explanations of the prevalence of host specialism, but empirical evidence for such trade-offs is rare. We propose an alternative theory based on basic features of the parasite life cycle: host selection and subsequent intrahost replication. We introduce a new concept of effective burst size that accounts for the fact that successful host selection does not guarantee intrahost replication. Our theory makes a general prediction that a parasite will expand its host range if its effective burst size is positive. An in silico model of bacteria-phage coevolution verifies our predictions and demonstrates that the tendency for relatively narrow host ranges in parasites can be explained even in the absence of trade-offs.IG was supported by a NERC Advanced Fellowship. IG and MS were also funded by a BBSRC
EEID grant
Semiclassical structure of chaotic resonance eigenfunctions
We study the resonance (or Gamow) eigenstates of open chaotic systems in the
semiclassical limit, distinguishing between left and right eigenstates of the
non-unitary quantum propagator, and also between short-lived and long-lived
states. The long-lived left (right) eigenstates are shown to concentrate as
on the forward (backward) trapped set of the classical dynamics.
The limit of a sequence of eigenstates is found
to exhibit a remarkably rich structure in phase space that depends on the
corresponding limiting decay rate. These results are illustrated for the open
baker map, for which the probability density in position space is observed to
have self-similarity properties.Comment: 4 pages, 4 figures; some minor corrections, some changes in
presentatio
Semiclassical Theory of Quantum Chaotic Transport: Phase-Space Splitting, Coherent Backscattering and Weak Localization
We investigate transport properties of quantized chaotic systems in the short
wavelength limit. We focus on non-coherent quantities such as the Drude
conductance, its sample-to-sample fluctuations, shot-noise and the transmission
spectrum, as well as coherent effects such as weak localization. We show how
these properties are influenced by the emergence of the Ehrenfest time scale
\tE. Expressed in an optimal phase-space basis, the scattering matrix
acquires a block-diagonal form as \tE increases, reflecting the splitting of
the system into two cavities in parallel, a classical deterministic cavity
(with all transmission eigenvalues either 0 or 1) and a quantum mechanical
stochastic cavity. This results in the suppression of the Fano factor for
shot-noise and the deviation of sample-to-sample conductance fluctuations from
their universal value. We further present a semiclassical theory for weak
localization which captures non-ergodic phase-space structures and preserves
the unitarity of the theory. Contrarily to our previous claim [Phys. Rev. Lett.
94, 116801 (2005)], we find that the leading off-diagonal contribution to the
conductance leads to the exponential suppression of the coherent backscattering
peak and of weak localization at finite \tE. This latter finding is
substantiated by numerical magnetoconductance calculations.Comment: Typos in central eqns corrected (this paper supersedes
cond-mat/0509186) 20page
The Dirichlet-to-Robin Transform
A simple transformation converts a solution of a partial differential
equation with a Dirichlet boundary condition to a function satisfying a Robin
(generalized Neumann) condition. In the simplest cases this observation enables
the exact construction of the Green functions for the wave, heat, and
Schrodinger problems with a Robin boundary condition. The resulting physical
picture is that the field can exchange energy with the boundary, and a delayed
reflection from the boundary results. In more general situations the method
allows at least approximate and local construction of the appropriate reflected
solutions, and hence a "classical path" analysis of the Green functions and the
associated spectral information. By this method we solve the wave equation on
an interval with one Robin and one Dirichlet endpoint, and thence derive
several variants of a Gutzwiller-type expansion for the density of eigenvalues.
The variants are consistent except for an interesting subtlety of
distributional convergence that affects only the neighborhood of zero in the
frequency variable.Comment: 31 pages, 5 figures; RevTe
Semiclassical Treatment of Diffraction in Billiard Systems with a Flux Line
In billiard systems with a flux line semiclassical approximations for the
density of states contain contributions from periodic orbits as well as from
diffractive orbits that are scattered on the flux line. We derive a
semiclassical approximation for diffractive orbits that are scattered once on a
flux line. This approximation is uniformly valid for all scattering angles. The
diffractive contributions are necessary in order that semiclassical
approximations are continuous if the position of the flux line is changed.Comment: LaTeX, 17 pages, 4 figure
Semiclassical form factor for spectral and matrix element fluctuations of multi-dimensional chaotic systems
We present a semiclassical calculation of the generalized form factor which
characterizes the fluctuations of matrix elements of the quantum operators in
the eigenbasis of the Hamiltonian of a chaotic system. Our approach is based on
some recently developed techniques for the spectral form factor of systems with
hyperbolic and ergodic underlying classical dynamics and f=2 degrees of
freedom, that allow us to go beyond the diagonal approximation. First we extend
these techniques to systems with f>2. Then we use these results to calculate
the generalized form factor. We show that the dependence on the rescaled time
in units of the Heisenberg time is universal for both the spectral and the
generalized form factor. Furthermore, we derive a relation between the
generalized form factor and the classical time-correlation function of the Weyl
symbols of the quantum operators.Comment: some typos corrected and few minor changes made; final version in PR
Exchange Interactions and High-Energy Spin States in Mn_12-acetate
We perform inelastic neutron scattering measurements on the molecular
nanomagnet Mn_12-acetate to measure the excitation spectrum up to 45meV (500K).
We isolate magnetic excitations in two groups at 5-6.5meV (60-75K) and
8-10.5meV (95-120K), with higher levels appearing only at 27meV (310K) and
31meV (360K). From a detailed characterization of the transition peaks we show
that all of the low-energy modes appear to be separate S = 9 excitations above
the S = 10 ground state, with the peak at 27meV (310K) corresponding to the
first S = 11 excitation. We consider a general model for the four exchange
interaction parameters of the molecule. The static susceptibility is computed
by high-temperature series expansion and the energy spectrum, matrix elements
and ground-state spin configuration by exact diagonalization. The theoretical
results are matched with experimental observation by inclusion of cluster
anisotropy parameters, revealing strong constraints on possible parameter sets.
We conclude that only a model with dominant exchange couplings J_1 ~ J_2 ~
5.5meV (65K) and small couplings J_3 ~ J_4 ~ 0.6meV (7K) is consistent with the
experimental data.Comment: 17 pages, 12 figure
Feasibility of an Outpatient Training Program after COVID-19
Long-term physical consequences of coronavirus disease 2019 (COVID-19) are currently being reported. As a result, the focus is turning towards interventions that support recovery after hospitalization. To date, the feasibility of an outpatient program for people recovering from COVID-19 has not been investigated. This study presents data for a physiotherapy-led, comprehensive outpatient pulmonary rehabilitation (PR) program. Patients were recruited after hospital discharge. Training consisted of twice weekly, interval-based aerobic cycle endurance (ACE) training, followed by resistance training (RT); 60â90 min per session at intensities of 50% peak work rate; education and physical activity coaching were also provided. Feasibility outcomes included: recruitment and dropout rates, number of training sessions undertaken, and tolerability for dose and training mode. Of the 65 patients discharged home during the study period, 12 were successfully enrolled onto the program. Three dropouts (25%) were reported after 11â19 sessions. Tolerability of interval-based training was 83% and 100% for exercise duration of ACE and RT, respectively; 92% for training intensity, 83% progressive increase of intensity, and 83% mode in ACE. We tentatively suggest from these preliminary findings that the PR protocol used may be both feasible, and confer benefits to a small subgroup of patients recovering from COVID-19
Developing SOEPsurvey and SOEPservice: The (Near) Future of the German Socio-Economic Panel Study (SOEP)
Das Sozio-oekonomische Panel (SOEP) ist als multidisziplinĂ€res Haushaltspanel, das Informationen zu allen Personen, die in einem Panel-Haushalt leben, erhebt und damit alle AltersjahrgĂ€nge abdeckt, nach 25 Jahren Laufzeit auch zu einer Kohorten- Studie geworden. Der zunehmende Erfolg der Forschungsinfrastruktur-Einrichtung SOEP speist sich in erster Linie daraus, dass die Analysekraft von LĂ€ngsschnittstudien mit jedem weiteren Erhebungsjahr zunimmt. Hinzu kommen im Falle des SOEP seit Beginn an eine lange Reihe von Innovationen bei der Erhebung, Datenaufbereitung und Nutzer-Service. Deswegen gilt es zu ĂŒberlegen, wie die wissenschaftliche Power des SOEP weiter gestĂ€rkt werden kann. Nicht zuletzt auch, da es fĂŒr neue, spezialisierte Panel-Studien (wie das Nationale Bildungspanel oder das DFG-geförderte Familienpanel PAIRFAM) eine Referenz und ggf. Verankerung der Hochrechnung darstellt. Zudem kann das SOEP kĂŒnftig eine gröĂere Rolle als ,,Kontroll-Stichprobe" fĂŒr Interventions-Studien spielen; etwa im Bereich der Kindheitsentwicklung. Auf diese neuen Rollen muss es vorbereitet sein. Die im SOEP in den letzten Jahren realisierten Erhebungsinnovationen wie z. B. die Inkorporation psychologischer Konzepte, physische Gesundheitsmessungen (Greifkraft), die Messung kognitiver FĂ€higkeiten und die Erprobung von Verhaltens- Experimenten werden in anderen Panel-Studien aufgegriffen und auf eine gröĂere Stichprobenbasis gestellt. Im UK wird mit ,,Understanding Society" ein Haushaltspanel mit 40.000 Haushalten begonnen; in den Niederlanden wird mit MESS ein Haushaltspanel von ĂŒber 5.000 Haushalten fĂŒr innovative Messmethoden zur VerfĂŒgung gestellt. Die Erhebungsinhalte des SOEP werden von den Forschungs- und Politikberatungs-Communities unverĂ€ndert stark nachgefragt. In UK hat ein fĂŒr ,,Understanding Society" breit angelegter Konsultationsprozess keine grundsĂ€tzlich neuen Befragungsinhalte zu Tage gefördert, die das SOEP nicht bereits enthĂ€lt oder die fĂŒr das SOEP ohnehin im GesprĂ€ch sind. Wichtiger als die ,,Entdeckung" völlig neuer Erhebungsinhalte ist das thematische wie zeitliche ,,Zuschneiden" der Details von Befragungsinhalten auf (zugespitzte) neue (theoretische) Fragestellungen und dabei gleichzeitig bewĂ€hrte sowie viel genutzte zentrale Befragungsinhalte und deren Befragungsrhythmen beizubehalten. Das ,,MaĂschneidern" von Erhebungsinhalten wird in den nĂ€chsten Jahren die eigentliche Herausforderung fĂŒr Infrastruktur- Erhebungen wie die PSID, ,,Understanding Society" und das SOEP sein. Bei den Erhebungsinhalten sollten die ,,RĂ€nder" des Lebenslaufs eine gröĂere Rolle spielen, da diese von Haushalts-Panels besonders gut erfasst werden können. Diese Verbesserungen der Erhebungen beziehen sich einerseits auf die fötale Phase von in das SOEP hineingeborenen Kindern und die (frĂŒhe) Kindheit, andererseits auf die letzte Lebensphase und das Sterben. In der Mitte des Lebenslaufs werden verbesserte Fragen zum Einkommen, Sparen und Vermögen sowie auch psychologische Konstrukte eine zentrale Rolle spielen, auĂerdem gezielte Fragen (event triggered questionnaires) in Verbindung mit zentralen Lebensereignissen wie z. B. EheschlieĂung, Scheidung, Eintritt in und Austritt aus Arbeitslosigkeit. Es wird die Etablierung einer SOEP-"Innovations-Stichprobe" vorbereitet, um theoriegeleitete Forschungsfragen gezielter unterstĂŒtzen zu können. Dazu wird es auch notwendig sein, neue Messkonzepte zu erproben (z. B. die Erhebung von Biomarkern, qualitative Erhebungen, aber auch Experimente und gezielte Interventionsstudien). Um die Power von LĂ€ngsschnittdaten von Anfang an fĂŒr die Innovations-Stichprobe ausnutzen zu können, ist geplant, zwei kleinere Teilstichproben des SOEP, die seit 1998 bzw. 2006 laufen (Subsamples E und H), in die Innovationsstichprobe zu ĂŒberfĂŒhren. Um die statistische Power langlaufender LĂ€ngsschnittdaten entscheidend zu verbessern, schĂ€tzen wir eine Mindestfallzahl von etwa 500 Personen pro Geburtsund Alterskohorte fĂŒr ausreichend ein. Um dieses Ziel zu erreichen, muss die Fallzahl des SOEP-Standard-Samples erhöht werden. Als ,,Nebeneffekt" werden dadurch wesentlich bessere Analysen fĂŒr relativ kleine Gruppen in der Bevölkerung möglich; etwa fĂŒr allein Erziehende oder bestimme Immigrantengruppen. AuĂerdem verbessern sich als weiterer ,,Nebeneffekt" auch regionale Analysemöglichkeiten, z. B. fĂŒr die meisten BundeslĂ€nder und in groĂen BundeslĂ€ndern bis hin zu Regierungsbezirken (oder Ă€hnlich abgegrenzten regionalen Einheiten). In letzter Zeit wird immer deutlicher, welche groĂe Bedeutung das SOEP als ,,Referenz-Datensatz" fĂŒr spezialisierte und vom SOEP völlig unabhĂ€ngige Erhebungen hat (neben Beobachtungsstudien, wie etwa Zwillings-Studien, auch Labor- und Interventions-Studien). Zur UnterstĂŒtzung dieser Funktion ist eine neue Art von Service, der in Deutschland bislang nicht vorgehalten wird, notwendig (Beratung von Spezial-Erhebungen; ggf. Datenaufbereitung von lĂ€ngsschnittlichen Spezial-Erhebungen), der auch in ein Datenservicezentrum eingebracht werden könnte. After 25 years as a multidisciplinary household panel containing information on all individuals residing in panel households and thus covering all age cohorts, the German Socio-Economic Panel (SOEP) has become a true cohort study as well. The increasing success of the SOEP research infrastructure comes above all from the increasing analytical power that longitudinal studies attain with each successive survey year. In the case of SOEP, a long series of innovations in surveying, data preparation, and user service have also played a major role. For this reason, it is important to consider how the scientific capacity of SOEP can be further enhanced-- not least of all since the SOEP can form a key point of reference (or "anchor") for new, specialized panel studies (such as the National Educational Panel and the family panel PAIRFAM, funded by the German Research Foundation). Furthermore SOEP can become a kind of "control sample" for intervention studies, for example, in the field of child development. The SOEP survey and its governance structures must be prepared for these new tasks. The numerous innovations introduced into SOEP in recent years--questions dealing with psychological concepts, physical health measures (grip strength), measures of cognitive capabilities, and behavioral experiments--have been incorporated into other panel studies as well, and thus provided with a larger sample base. In the UK, the "Understanding Society" household panel study was launched with 40,000 households; in the Netherlands, the MESS household panel study of over 5,000 households offered a new basis for testing innovative measurement methods. The results of the SOEP survey are in continuing high demand in the research and policy advisory community. From our point of view, the large-scale consultation process conducted to define the content of the UK survey "Understanding Society" failed to identify any fundamentally new survey content that the SOEP either did not already contain or that was not already being discussed for the SOEP. More important than "discovering" entirely new survey areas is "tailoring" the details of existing survey content to address new, more specific (theoretical) questions, and thus maintaining proven and widely used elements of survey content. The "tailoring" of survey content will be the real challenge facing infrastructure surveys like PSID, "Understanding Society," and the SOEP in the coming years. In the future, the "margins" of the life course should play a stronger role in survey content, since household panels are able to provide outstanding data of these life phases. The SOEP, and other household panel surveys, can be improved, on the one hand, by including the fetal phase of life and early childhood for children born into the panel, and on the other, by including late life and death. In the middle of the life course, improved questions on income, savings, and wealth as well as psychological constructs will play a central role, as will specific questions (in "eventtriggered" questionnaires) on central life occurrences such as marriage, divorce, and entry into and exit from unemployment. Current plans for SOEP foresee the addition of an "Innovation Sample" that will make it possible to better address theory-based research questions required for testing new measurement concepts (e.g., the surveying of biomarkers, qualitative surveys, but also experiments and targeted intervention studies). In order to exploit the power of longitudinal data from the outset, we plan to incorporate two smaller SOEP subsamples that have been running since 1998 and 2006 (Subsamples E and H, respectively) into the Innovation Sample. In order to decisively improve the statistical power of long-term longitudinal data, we believe that a minimum case number of about 500 persons per birth and age cohort is required. In order to reach this goal, the case number in the SOEP standard samples needs to be increased. A positive side-effect of this enlargement would be a significantly improved potential for analyses of relatively small groups within the population: for example, lone parents or specific immigrant groups. Another positive side-effect would be an improved potential for regional analyses: for example, for the majority of federal states. In recent times, the importance of SOEP as a "reference dataset" for specialized surveys which are independent from SOEP (observational studies such as twin studies, and laboratory and intervention studies) has become strikingly evident. To enhance this important function, new types of service are needed (advice on special surveys, possibly also data preparation for special surveys), which could become part of a Data Service Center.Household Panels, German Socio-Economic Panel Study, SOEP
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