461 research outputs found
Quantum Parton Shower with Kinematics
Parton showers which can efficiently incorporate quantum interference effects
have been shown to be run efficiently on quantum computers. However, so far
these quantum parton showers did not include the full kinematical information
required to reconstruct an event, which in classical parton showers requires
the use of a veto algorithm. In this work, we show that adding one extra
assumption about the discretization of the evolution variable allows to
construct a quantum veto algorithm, which reproduces the full quantum
interference in the event, and allows to include kinematical effects. We
finally show that for certain initial states the quantum interference effects
generated in this veto algorithm are classically tractable, such that an
efficient classical algorithm can be devised.Comment: 14 pages, 8 figure
Gravitational energy in a small region for the modified Einstein and Landau-Lifshitz pseudotensors
The purpose of the classical Einstein and Landau-Lifshitz pseudotensors is
for determining the gravitational energy. Neither of them can guarantee a
positive energy in holonomic frames. In the small sphere approximation, it has
been required that the quasilocal expression for the gravitational
energy-momentum density should be proportional to the Bel-Robinson tensor
. However, we propose a new tensor
which is the sum of certain tensors
and , it has certain properties
so that it gives the same gravitational "energy-momentum" content as
does. Moreover, we show that a modified Einstein
pseudotensor turns out to be one of the Chen-Nester quasilocal expressions,
while the modified Landau-Lifshitz pseudotensor becomes the Papapetrou
pseudotensor; these two modified pseudotensors have positive gravitational
energy in a small region.Comment:
Thermoelectric spin voltage in graphene
In recent years, new spin-dependent thermal effects have been discovered in
ferromagnets, stimulating a growing interest in spin caloritronics, a field
that exploits the interaction between spin and heat currents. Amongst the most
intriguing phenomena is the spin Seebeck effect, in which a thermal gradient
gives rise to spin currents that are detected through the inverse spin Hall
effect. Non-magnetic materials such as graphene are also relevant for spin
caloritronics, thanks to efficient spin transport, energy-dependent carrier
mobility and unique density of states. Here, we propose and demonstrate that a
carrier thermal gradient in a graphene lateral spin valve can lead to a large
increase of the spin voltage near to the graphene charge neutrality point. Such
an increase results from a thermoelectric spin voltage, which is analogous to
the voltage in a thermocouple and that can be enhanced by the presence of hot
carriers generated by an applied current. These results could prove crucial to
drive graphene spintronic devices and, in particular, to sustain pure spin
signals with thermal gradients and to tune the remote spin accumulation by
varying the spin-injection bias
Spin Seebeck insulator
Thermoelectric generation is an essential function of future energy-saving
technologies. However, this generation has been an exclusive feature of
electric conductors, a situation which inflicts a heavy toll on its
application; a conduction electron often becomes a nuisance in thermal design
of devices. Here we report electric-voltage generation from heat flowing in an
insulator. We reveal that, despite the absence of conduction electrons, a
magnetic insulator LaY2Fe5O12 converts a heat flow into spin voltage. Attached
Pt films transform this spin voltage into electric voltage by the inverse spin
Hall effect. The experimental results require us to introduce thermally
activated interface spin exchange between LaY2Fe5O12 and Pt. Our findings
extend the range of potential materials for thermoelectric applications and
provide a crucial piece of information for understanding the physics of the
spin Seebeck effect.Comment: 19 pages, 5 figures (including supplementary information
Comparing non-fullerene acceptors with fullerene in polymer solar cells: a case study with FTAZ and PyCNTAZ
Non-fullerene acceptors (NFAs) are becoming a serious contender to fullerene-based electron acceptors in organic photovoltaics, due to their structural versatility and easily tunable optical and electronic properties. However, NFA-based solar cells often have a decreased short-circuit current (Jsc) and fill factor (FF) compared to their fullerene-based counterparts. Here, we investigate the fundamental causes of this decrease in the performance of solar cells using a non-fullerene acceptor (SF-PDI2) paired with two polymer donors, FTAZ and PyCNTAZ, compared with their fullerene-based counterparts. Through a number of experimental techniques and morphological studies, we show that the SF-PDI2-based solar cells suffer from insufficient charge generation, transport, and collection when compared with the PCBM-based solar cells. The SF-PDI2-based solar cells show increased bimolecular recombination, which, together with other recombination loss mechanisms in these cells, causes a significant decrease in their Jsc and FF. Notably, the less pure domains, low electron mobility (on the order of 10−5 cm2 V−1 s−1), and imbalanced mobility (in regard to the hole mobility) further explain the low FF. On the other hand, the higher open-circuit voltage (Voc) in the SF-PDI2 devices is mainly due to the increase in the CT state energy. It is worth mentioning that the PyCNTAZ-based devices show an ultralow charge separation energy (ΔECS), close to 0 eV. Our results demonstrate that further increasing the mobility (both of electrons and holes) in these NFA-based solar cells would be a viable approach to further enhance the efficiency of these new types of solar cells, ideally, without losing the high Voc of such cells
Spin Caloritronics
This is a brief overview of the state of the art of spin caloritronics, the
science and technology of controlling heat currents by the electron spin degree
of freedom (and vice versa).Comment: To be published in "Spin Current", edited by S. Maekawa, E. Saitoh,
S. Valenzuela and Y. Kimura, Oxford University Pres
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Brief Online Self-help Exercises for Postnatal Women to Improve Mood: A Pilot Study
OBJECTIVES: Giving birth and adjusting to a new baby can be difficult and stressful for new mothers. Negative mood may occur during this time and can affect women, their parenting and the infant's development. This pilot study evaluated a brief online self-help intervention designed to promote positive mood in mothers of babies and toddlers.
METHODS: Women in the UK who had given birth within the previous 18 months were randomly allocated to the online self-help intervention (n = 40) or active comparison group exercise (n = 40) which was matched for time and structure. Mood was measured before and after the intervention. Acceptability was examined at the end of the trial.
RESULTS: The self-help intervention was acceptable to the majority of women and significantly increased positive mood compared to the comparison condition. This effect persisted after controlling for self-esteem, anxiety and depression. These results suggest that a simple self-help intervention focused on changing beliefs about oneself as a mother can have an immediate impact on women's mood.
CONCLUSIONS FOR PRACTICE: Further research is need to see whether these improvements continue long-term and what processes underlie these improvements
Modeling-Dependent Protein Characterization of the Rice Aldehyde Dehydrogenase (ALDH) Superfamily Reveals Distinct Functional and Structural Features
The completion of the rice genome sequence has made it possible to identify and characterize new genes and to perform comparative genomics studies across taxa. The aldehyde dehydrogenase (ALDH) gene superfamily encoding for NAD(P)+-dependent enzymes is found in all major plant and animal taxa. However, the characterization of plant ALDHs has lagged behind their animal- and prokaryotic-ALDH homologs. In plants, ALDHs are involved in abiotic stress tolerance, male sterility restoration, embryo development and seed viability and maturation. However, there is still no structural property-dependent functional characterization of ALDH protein superfamily in plants. In this paper, we identify members of the rice ALDH gene superfamily and use the evolutionary nesting events of retrotransposons and protein-modeling–based structural reconstitution to report the genetic and molecular and structural features of each member of the rice ALDH superfamily in abiotic/biotic stress responses and developmental processes. Our results indicate that rice-ALDHs are the most expanded plant ALDHs ever characterized. This work represents the first report of specific structural features mediating functionality of the whole families of ALDHs in an organism ever characterized
Breast Cancer Cells Induce Cancer-Associated Fibroblasts to Secrete Hepatocyte Growth Factor to Enhance Breast Tumorigenesis
It has been well documented that microenvironment consisting of stroma affects breast cancer progression. However, the mechanisms by which cancer cells and fibroblasts, the major cell type in stroma, interact with each other during tumor development remains to be elucidated. Here, we show that the human cancer-associated fibroblasts (CAFs) had higher activity in enhancing breast tumorigenecity compared to the normal tissue-associated fibroblasts (NAFs) isolated from the same patients. The expression level of hepatocyte growth factor (HGF) in these fibroblasts was positively correlated with their ability to enhance breast tumorigenesis in mice. Deprivation of HGF using a neutralizing antibody reduced CAF-mediated colony formation of human breast cancer cells, indicating that CAFs enhanced cancer cell colony formation mainly through HGF secretion. Co-culture with human breast cancer MDA-MB-468 cells in a transwell system enhanced NAFs to secret HGF as well as promote tumorigenecity. The newly gained ability of these “educated” NAFs became irreversible after continuing this process till fourth passage. These results suggested that breast cancer cells could alter the nature of its surrounding fibroblasts to secrete HGF to support its own progression through paracrine signaling
The state of the Martian climate
60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes
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