1,691 research outputs found
Microscopic energy flows in disordered Ising spin systems
An efficient microcanonical dynamics has been recently introduced for Ising
spin models embedded in a generic connected graph even in the presence of
disorder i.e. with the spin couplings chosen from a random distribution. Such a
dynamics allows a coherent definition of local temperatures also when open
boundaries are coupled to thermostats, imposing an energy flow. Within this
framework, here we introduce a consistent definition for local energy currents
and we study their dependence on the disorder. In the linear response regime,
when the global gradient between thermostats is small, we also define local
conductivities following a Fourier dicretized picture. Then, we work out a
linearized "mean-field approximation", where local conductivities are supposed
to depend on local couplings and temperatures only. We compare the approximated
currents with the exact results of the nonlinear system, showing the
reliability range of the mean-field approach, which proves very good at high
temperatures and not so efficient in the critical region. In the numerical
studies we focus on the disordered cylinder but our results could be extended
to an arbitrary, disordered spin model on a generic discrete structures.Comment: 12 pages, 6 figure
Classical simulation of measurement-based quantum computation on higher-genus surface-code states
We consider the efficiency of classically simulating measurement-based
quantum computation on surface-code states. We devise a method for calculating
the elements of the probability distribution for the classical output of the
quantum computation. The operational cost of this method is polynomial in the
size of the surface-code state, but in the worst case scales as in the
genus of the surface embedding the code. However, there are states in the
code space for which the simulation becomes efficient. In general, the
simulation cost is exponential in the entanglement contained in a certain
effective state, capturing the encoded state, the encoding and the local
post-measurement states. The same efficiencies hold, with additional
assumptions on the temporal order of measurements and on the tessellations of
the code surfaces, for the harder task of sampling from the distribution of the
computational output.Comment: 21 pages, 13 figure
Efficient estimation of energy transfer efficiency in light-harvesting complexes
The fundamental physical mechanisms of energy transfer in photosynthetic
complexes is not yet fully understood. In particular, the degree of efficiency
or sensitivity of these systems for energy transfer is not known given their
non-perturbative and non-Markovian interactions with proteins backbone and
surrounding photonic and phononic environments. One major problem in studying
light-harvesting complexes has been the lack of an efficient method for
simulation of their dynamics in biological environments. To this end, here we
revisit the second-order time-convolution (TC2) master equation and examine its
reliability beyond extreme Markovian and perturbative limits. In particular, we
present a derivation of TC2 without making the usual weak system-bath coupling
assumption. Using this equation, we explore the long time behaviour of exciton
dynamics of Fenna-Matthews-Olson (FMO) protein complex. Moreover, we introduce
a constructive error analysis to estimate the accuracy of TC2 equation in
calculating energy transfer efficiency, exhibiting reliable performance for
environments with weak and intermediate memory and strength. Furthermore, we
numerically show that energy transfer efficiency is optimal and robust for the
FMO protein complex of green sulphur bacteria with respect to variations in
reorganization energy and bath correlation time-scales.Comment: 16 pages, 9 figures, modified version, updated appendices and
reference lis
Architecture, structural and tectonic significance of the Seagap fault (offshore Tanzania) in the framework of the East African Rift
The Southeastern portion of the East African Rift System reactivates Mesozoic transform faults marking the separation of Madagascar from Africa in the Western Indian Ocean. Earlier studies noted the reactivation of the Davie Fracture Zone in oceanic lithosphere as a seismically active extensional fault, and new 3D seismic reflection data and exploration wells provide unprecedented detail on the kinematics of the sub-parallel Seagap fault zone in continental/transitional crust landward of the ocean-continent transition. We reconstruct the evolution of the seismically active Seagap fault zone, a 400-km-long crustal structure affecting the Tanzania margin, from the late Eocene to the present day. The Seagap fault zone is represented by large-scale localized structures affecting the seafloor and displaying growth geometries across most of the Miocene sediments. The continuous tectonic activity evident by our seismic mapping, as well as 2D deep seismic data from literature, suggests that from the Middle-Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and coeval with, the dextral Davie Fracture Zone. The Seagap fault then remained active after the cessation of both seafloor spreading in the Somali basin and strike-slip activity on the Davie Fracture Zone, till nowaday. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate that those restraining bends are generated by strike-slip reactivation of Cretaceous structures till the Miocene. Finally based on the interpretation of edge-enhanced reflection seismic surfaces and seafloor data, we shows that, by the late Neogene, the Seagap fault zone switched to normal fault behaviour. We discuss the Seagap fault's geological and kinematic significance through time and its current role within the microplate system in the framework of the East African rift, as well as implications for the evolution and re-activation of structures along sheared margins. The newly integrated datasets reveal the polyphase deformation of this margin, highlighting its complex evolution and the implications for depositional fairways and structural trap and seal changes through time, as well as potential hazards
Influence of supramolecular forces on the linear viscoelasticity of gluten
Stress relaxation behavior of hydrated gluten networks was investigated by means of rheometry combined with μ-computed tomography (μ-CT) imaging. Stress relaxation behavior was followed over a wide temperature range (0–70 °C). Modulation of intermolecular bonds was achieved with urea or ascorbic acid in an effort to elucidate the presiding intermolecular interactions over gluten network relaxation. Master curves of viscoelasticity were constructed, and relaxation spectra were computed revealing three relaxation regimes for all samples. Relaxation commences with a well-defined short-time regime where Rouse-like modes dominate, followed by a power law region displaying continuous relaxation concluding in a terminal zone. In the latter zone, poroelastic relaxation due to water migration in the nanoporous structure of the network also contributes to the stress relief in the material. Hydrogen bonding between adjacent protein chains was identified as the determinant force that influences the relaxation of the networks. Changes in intermolecular interactions also resulted in changes in microstructure of the material that was also linked to the relaxation behavior of the networks
Shot noise in ferromagnetic single electron tunneling devices
Frequency dependent current noise in ferromagnetic double junctions with
Coulomb blockade is studied theoretically in the limit of sequential tunneling.
Two different relaxation processes are found in the correlations between spin
polarized tunneling currents; low frequency spin fluctuations and high
frequency charge fluctuations. Spin accumulation in strongly asymmetric
junctions is shown to lead to a negative differential resistance. We also show
that large spin noise activated in the range of negative differential
resistance gives rise to a significant enhancement of the current noise.Comment: 8 pages, 13 eps-figures include
Zero Frequency Current Noise for the Double Tunnel Junction Coulomb Blockade
We compute the zero frequency current noise numerically and in several limits
analytically for the coulomb blockade problem consisting of two tunnel
junctions connected in series. At low temperatures over a wide range of
voltages, capacitances, and resistances it is shown that the noise measures the
variance in the number of electrons in the region between the two tunnel
junctions. The average current, on the other hand, only measures the mean
number of electrons. Thus, the noise provides additional information about
transport in these devices which is not available from measuring the current
alone.Comment: 33 pages, 10 figure
Health-Related Quality of Life in Relation to Obesity Grade, Type 2 Diabetes, Metabolic Syndrome and Inflammation
Health-related quality of life (HR-QoL) may be compromised in obese individuals, depending on the presence of other complications. The aim of this study is to assess the effect of obesity-related conditions on HR-QoL. These conditions are i) grade of obesity with and without type 2 diabetes (T2D), ii) metabolic syndrome (MetS), and iii) level of inflammation.From the Dutch LifeLines Cohort Study we included 13,686 obese individuals, aged 18-80 years. HR-QoL was measured with the RAND 36-Item Health Survey which encompasses eight health domains. We calculated the percentage of obese individuals with poor HR-QoL, i.e. those scoring below the domain and sex specific cut-off value derived from the normal weight population. Logistic regression analysis was used to calculate the probability of having poor domain scores according to the conditions under study.Higher grades of obesity and the additional presence of T2D were associated with lower HR-QoL, particularly in the domains physical functioning (men: odds ratios (ORs) 1.48-11.34, P<0.005, and women: ORs 1.66-5.05, P<0.001) and general health (men: ORs 1.44-3.07, P<0.005, and women: ORs 1.36-3.73, P<0.001). A higher percentage of obese individuals with MetS had a poor HR-QoL than those without MetS. Furthermore, we observed a linear trend between inflammation and the percentage of obese individuals with poor scores on the HR-QoL domains. Individuals with MetS were more likely to have poor scores in the domains general health, vitality, social functioning and role limitations due to emotional problems. Obese women with increased inflammation levels were more likely to have poor scores on all domains except role limitations due to emotional problems and mental health.The impact of obesity on an individual's quality of life is enhanced by grade of obesity, T2D, MetS and inflammation and are mainly related to reduced physical health. The mental well-being is less often impaired
Spin effects in single electron tunneling
An important consequence of the discovery of giant magnetoresistance in
metallic magnetic multilayers is a broad interest in spin dependent effects in
electronic transport through magnetic nanostructures. An example of such
systems are tunnel junctions -- single-barrier planar junctions or more complex
ones. In this review we present and discuss recent theoretical results on
electron and spin transport through ferromagnetic mesoscopic junctions
including two or more barriers. Such systems are also called ferromagnetic
single-electron transistors. We start from the situation when the central part
of a device has the form of a magnetic (or nonmagnetic) metallic nanoparticle.
Transport characteristics reveal then single-electron charging effects,
including the Coulomb staircase, Coulomb blockade, and Coulomb oscillations.
Single-electron ferromagnetic transistors based on semiconductor quantum dots
and large molecules (especially carbon nanotubes) are also considered. The main
emphasis is placed on the spin effects due to spin-dependent tunnelling through
the barriers, which gives rise to spin accumulation and tunnel
magnetoresistance. Spin effects also occur in the current-voltage
characteristics, (differential) conductance, shot noise, and others. Transport
characteristics in the two limiting situations of weak and strong coupling are
of particular interest. In the former case we distinguish between the
sequential tunnelling and cotunneling regimes. In the strong coupling regime we
concentrate on the Kondo phenomenon, which in the case of transport through
quantum dots or molecules leads to an enhanced conductance and to a pronounced
zero-bias Kondo peak in the differential conductance.Comment: topical review (36 figures, 65 pages), to be published in J. Phys.:
Condens. Matte
Wearable Haptic Devices for Gait Re-education by Rhythmic Haptic Cueing
This research explores the development and evaluation of wearable haptic devices for gait sensing and rhythmic haptic cueing in the context of gait re-education for people with neurological and neurodegenerative conditions. Many people with long-term neurological and neurodegenerative conditions such as Stroke, Brain Injury, Multiple Sclerosis or Parkinson’s disease suffer from impaired walking gait pattern. Gait improvement can lead to better fluidity in walking, improved health outcomes, greater independence, and enhanced quality of life. Existing lab-based studies with wearable devices have shown that rhythmic haptic cueing can cause immediate improvements to gait features such as temporal symmetry, stride length, and walking speed. However, current wearable systems are unsuitable for self-managed use for in-the-wild applications with people having such conditions. This work aims to investigate the research question of how wearable haptic devices can help in long-term gait re-education using rhythmic haptic cueing. A longitudinal pilot study has been conducted with a brain trauma survivor, providing rhythmic haptic cueing using a wearable haptic device as a therapeutic intervention for a two-week period. Preliminary results comparing pre and post-intervention gait measurements have shown improvements in walking speed, temporal asymmetry, and stride length. The pilot study has raised an array of issues that require further study. This work aims to develop and evaluate prototype systems through an iterative design process to make possible the self-managed use of such devices in-the-wild. These systems will directly provide therapeutic intervention for gait re-education, offer enhanced information for therapists, remotely monitor dosage adherence and inform treatment and prognoses over the long-term. This research will evaluate the use of technology from the perspective of multiple stakeholders, including clinicians, carers and patients. This work has the potential to impact clinical practice nationwide and worldwide in neuro-physiotherapy
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