Microscopic formula for transport coefficients of causal hydrodynamics

The Green-Kubo-Nakano formula should be modified in relativistic hydrodynamics because of the problem of acausality and the breaking of sum rules. In this work, we propose a formula to calculate the transport coefficients of causal hydrodynamics based on the projection operator method. As concrete examples, we derive the expressions for the diffusion coefficient, the shear viscosity coefficient, and corresponding relaxation times.Comment: 4 pages, title was modified, final version published in Phys. Rev.

Exponential decay in a spin bath

We show that the coherence of an electron spin interacting with a bath of nuclear spins can exhibit a well-defined purely exponential decay for special (`narrowed') bath initial conditions in the presence of a strong applied magnetic field. This is in contrast to the typical case, where spin-bath dynamics have been investigated in the non-Markovian limit, giving super-exponential or power-law decay of correlation functions. We calculate the relevant decoherence time T_2 explicitly for free-induction decay and find a simple expression with dependence on bath polarization, magnetic field, the shape of the electron wave function, dimensionality, total nuclear spin I, and isotopic concentration for experimentally relevant heteronuclear spin systems.Comment: 4+ pages, 3 figures; v2: 9 pages, 3 figures (added four appendices with extensive technical details, version to appear in Phys. Rev. B

Well-being in Healthcare: Psychological Well-Being, Burnout, and Work Engagement in Long-Term Care Employees

The Job Demands-Resources (JD-R) model posits that both job demands and job resources affect employee well-being, including the experience of burnout or work engagement. More recent studies adding to the model suggest that personal resources also contribute to these work-related outcomes. A personal resource that has not been examined in the JD-R model is psychological wellbeing (PWB), which encompasses thriving through the existential challenges of life to actualize human potential, and reflects qualities of self-acceptance, positive relations with others, personal growth, purpose in life, environmental mastery, and autonomy. The purpose of this study is to extend the JD-R model by examining the potential of PWB to inform the model. This work was done within the Canadian LTC context, which has not yet been examined using this model. A convenience sample of 327 LTC employees (110 nurses and 214 nursing assistants; three people chose not to disclose their status), completed a questionnaire assessing burnout, work engagement, job demands, job resources, and PWB. Simultaneous regression was used to examine the relationship between job demands and burnout, and job resources and work engagement, according to the JD-R model. Moderation analysis using PROCESS (Hayes, 2013) was used to ascertain whether PWB contributed to the model as a moderator of either burnout or engagement. Findings were as follows: (i) certain job demands (i.e., workload, emotion load, and role conflict) contribute significantly to burnout in LTC; (ii) certain job resources (i.e., autonomy, relationship with coworkers, relationship with supervisor, and participation) contribute significantly to work engagement in LTC; (iii) PWB moderates the relationship between job demands and burnout; (iv) PWB does not moderate the relationship between job resources and work engagement. These results extend the JD-R model to the Canadian LTC setting. They provide information about the kinds of demands and resources that relate to burnout and work engagement in LTC, and they confirm that PWB is an important personal resource for LTC nurses and nursing assistants, since it moderates (buffers) the relationship between job demands and burnout. These results have implications for promoting work engagement and reducing the likelihood of burnout in LTC

Microscopic Derivation of Causal Diffusion Equation using Projection Operator Method

We derive a coarse-grained equation of motion of a number density by applying the projection operator method to a non-relativistic model. The derived equation is an integrodifferential equation and contains the memory effect. The equation is consistent with causality and the sum rule associated with the number conservation in the low momentum limit, in contrast to usual acausal diffusion equations given by using the Fick's law. After employing the Markov approximation, we find that the equation has the similar form to the causal diffusion equation. Our result suggests that current-current correlations are not necessarily adequate as the definition of diffusion constants.Comment: 10 pages, 1 figure, Final version published in Phys. Rev.

Free-induction decay and envelope modulations in a narrowed nuclear spin bath

We evaluate free-induction decay for the transverse components of a localized electron spin coupled to a bath of nuclear spins via the Fermi contact hyperfine interaction. Our perturbative treatment is valid for special (narrowed) bath initial conditions and when the Zeeman energy of the electron $b$ exceeds the total hyperfine coupling constant $A$: $b>A$. Using one unified and systematic method, we recover previous results reported at short and long times using different techniques. We find a new and unexpected modulation of the free-induction-decay envelope, which is present even for a purely isotropic hyperfine interaction without spin echoes and for a single nuclear species. We give sub-leading corrections to the decoherence rate, and show that, in general, the decoherence rate has a non-monotonic dependence on electron Zeeman splitting, leading to a pronounced maximum. These results illustrate the limitations of methods that make use of leading-order effective Hamiltonians and re-exponentiation of short-time expansions for a strongly-interacting system with non-Markovian (history-dependent) dynamics.Comment: 13 pages, 9 figure

Dynamical typicality of quantum expectation values

We show that the vast majority of all pure states featuring a common expectation value of some generic observable at a given time will yield very similar expectation values of the same observable at any later time. This is meant to apply to Schroedinger type dynamics in high dimensional Hilbert spaces. As a consequence individual dynamics of expectation values are then typically well described by the ensemble average. Our approach is based on the Hilbert space average method. We support the analytical investigations with numerics obtained by exact diagonalization of the full time-dependent Schroedinger equation for some pertinent, abstract Hamiltonian model. Furthermore, we discuss the implications on the applicability of projection operator methods with respect to initial states, as well as on irreversibility in general.Comment: 4 pages, 1 figure, accepted for publication in Phys. Rev. Let

Singlet-triplet decoherence due to nuclear spins in a double quantum dot

We have evaluated hyperfine-induced electron spin dynamics for two electrons confined to a double quantum dot. Our quantum solution accounts for decay of a singlet-triplet correlator even in the presence of a fully static nuclear spin system, with no ensemble averaging over initial conditions. In contrast to an earlier semiclassical calculation, which neglects the exchange interaction, we find that the singlet-triplet correlator shows a long-time saturation value that differs from 1/2, even in the presence of a strong magnetic field. Furthermore, we find that the form of the long-time decay undergoes a transition from a rapid Gaussian to a slow power law ($\sim 1/t^{3/2}$) when the exchange interaction becomes nonzero and the singlet-triplet correlator acquires a phase shift given by a universal (parameter independent) value of $3\pi/4$ at long times. The oscillation frequency and time-dependent phase shift of the singlet-triplet correlator can be used to perform a precision measurement of the exchange interaction and Overhauser field fluctuations in an experimentally accessible system. We also address the effect of orbital dephasing on singlet-triplet decoherence, and find that there is an optimal operating point where orbital dephasing becomes negligible.Comment: 12 pages, 4 figure

Local forest structure variability increases resilience to wildfire in dry western U.S. coniferous forests.

A 'resilient' forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine-scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long-lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that greater variability in forest structure increases resilience by reducing rates of fire-induced tree mortality and that the scale of this effect is local, manifesting at the smallest spatial extent of forest structure tested (90 × 90 m). Resilience of these forests is likely compromised by structural homogenisation from a century of fire suppression, but could be restored with management that increases forest structural variability

Inkwisatoriese en akkusatoriese elemente in die Amerikaanse pleitonderhandelingsproses: rigtingwyser of waarskuwingsteken?

Uit teks: Dit word algemeen aanvaar dat die prosedure van pleitonderhandelinge die hele strafproses hervorm het en is die belangrikste hiervan dat koste bespaar word en tyd meer effektief gebruik kan word. Dit dien as belangrike middel tot beskikking van die aanklaer en die verdediging. Pleitonderhandelinge kan ook bydra tot uitskakeling van onskuldigbevindings by ’n verhoor op bloot ’n tegniese punt. Die prosedure beperk ook tot ’n groot mate die omvang van regsprekende beamptes se diskresie by vonnisoplegging en bring mee dat die beskuldigde persoonlik ook by die proses betrek word

Response-theory for nonresonant hole burning: Stochastic dynamics

Using non-linear response theory the time signals relevant for nonresonant spectral hole burning are calculated. The step-reponse function following the application of a high amplitude ac field (pump) and an intermediate waiting period is shown to be the sum of the equilibrium integrated response and a modification due to the preparation via ac irradiation. Both components are calculated for a class of stochastic dipole reorientation models. The results indicate that the method can be used for a clearcut distinction of homogeneously and heterogeneously broadened susceptibilities as they occur in the relaxation of supercooled liquids or other disordered materials. This is because only in the heterogeneous case is a frequency selective modification of the response possible.Comment: revised version, 7 pages, 2 figure