5,674 research outputs found
Optically-controlled long-term storage and release of thermal energy in phase-change materials
Thermal energy storage offers enormous potential for a wide range of energy technologies. Phase-change materials offer state-of-the-art thermal storage due to high latent heat. However, spontaneous heat loss from thermally charged phase-change materials to cooler surroundings occurs due to the absence of a significant energy barrier for the liquid-solid transition. This prevents control over the thermal storage, and developing effective methods to address this problem has remained an elusive goal. Herein, we report a combination of photo-switching dopants and organic phase-change materials as a way to introduce an activation energy barrier for phase-change materials solidification and to conserve thermal energy in the materials, allowing them to be triggered optically to release their stored latent heat. This approach enables the retention of thermal energy (about 200âJâgâ»Âč) in the materials for at least 10âh at temperatures lower than the original crystallization point, unlocking opportunities for portable thermal energy storage systems
Two-dimensional covalent triazine framework as an ultrathin-film nanoporous membrane for desalination
We computationally demonstrate that two-dimensional covalent triazine frameworks (CTFs) provide opportunities in water desalination. By varying the chemical building blocks, the pore structure, chemistry, and membrane performance can be designed, leading to two orders of magnitude higher water permeability than polyamide membranes while maintaining excellent ability to reject salts.Netherlands Organization for Scientific ResearchUnited States. Dept. of Energy (Contract No. DE-AC02-05CH11231)Deshpande Center for Technological Innovatio
Multilayer Nanoporous Graphene Membranes for Water Desalination
While single-layer nanoporous graphene (NPG) has shown promise as a reverse osmosis (RO) desalination membrane, multilayer graphene membranes can be synthesized more economically than the single-layer material. In this work, we build upon the knowledge gained to date toward single-layer graphene to explore how multilayer NPG might serve as a RO membrane in water desalination using classical molecular dynamic simulations. We show that, while multilayer NPG exhibits similarly promising desalination properties to single-layer membranes, their separation performance can be designed by manipulating various configurational variables in the multilayer case. This work establishes an atomic-level understanding of the effects of additional NPG layers, layer separation, and pore alignment on desalination performance, providing useful guidelines for the design of multilayer NPG membranes.National Science Foundation (U.S.) (grant number ACI-1053575)Netherlands Organization for Scientific Research (NWO
Measurement of sin2beta in tree-dominated B0-decays and ambiguity removal
The most recent results from the B-factories on the time-dependent CP
asymmetries measured in B0-decays mediated by b --> c c(bar) s
quark-transitions are reviewed. The Standard Model interpretation of the
results in terms of the parameter sin2beta leads to a four-fold ambiguity on
the unitarity triangle beta which can be reduced to a two-fold ambiguity by
measuring the sign of the parameter cos2beta. The results on cos2beta obtained
so far are reviewed.Comment: 6 pages, 3 postscript figues, contributed to the Proceedings of
Beauty200
Giving to Government: Voluntary Taxation in the Lab
In the United States, there is widespread antipathy toward taxation, yet at the same time there are substantial voluntary donations to nonprofit organizations with missions that are parallel to those of many government agencies. In this paper we compare giving in the form of voluntary taxes paid to government agencies with giving in the form of voluntary donations to nonprofit organizations that have similar missions. In a laboratory experimental setting, subjects are given an endowment, and are given the opportunity to donate any part of the endowment to a government agency or to a nonprofit organization. We compare levels of giving to private and government organizations for four different causes (cancer research, disaster relief, education, and parks and wildlife) at three levels of government (federal, state and local). Within a session, subjects make 12 decisions: they complete all six separate decisions for each of two causes, selected randomly from the four listed above. We find that people are not averse to giving to government. On average, they give 22 percent of their budget to government when anonymity is ensured and giving is completely voluntary. However, they do show a preference for nonprofit charities by giving higher amounts for most causes and levels of government. The willingness to give is influenced by the cause and level of the organization, as well as perceptions of the organization
Heavy particle electroweak loop effects in extra-dimensional models with bulk neutrinos
One way to detect the presence of new particles in theories beyond the
standard model is through their contribution to electroweak loop effects. We
comment on the importance of a consistent inclusion of their mixing angles to
ensure that the physical requirement of heavy particle decoupling is fulfilled.
We illustrate our points by a detailed discussion of the lepton flavor changing
effect mu-e-gamma, investigated recently by Kitano, in the Randall-Sundrum
model. Our remarks are equally applicable to models with large compactified
dimensions where bulk neutrinos are introduced to account for the observed
neutrino oscillations.Comment: 13 pages; new citations added in Ref [3] and [11
Trapping Penguins with Entangled B Mesons
The first direct observation of time-reversal (T) violation in the
system has been reported by the BaBar collaboration, employing the method of
Bauls and Bernab\'eu. Given this, we generalize their
analysis of the time-dependent T-violating asymmetry () to consider
different choices of CP tags for which the dominant amplitudes have the same
weak phase. As one application, we find that it is possible to measure
departures from the universality of directly. If
is universal, as in the Standard Model, the method permits the direct
determination of penguin effects in these channels. Our method, although no
longer a strict test of T, can yield tests of the universality,
or, alternatively, of penguin effects, of much improved precision even with
existing data sets.Comment: 11 pages, 2 figures; refs. added; reframed with expanded discussions;
version to appear in PLB; Metadata abstract updated onl
Exclusive B-> M \nu \bar{\nu} (M= \pi, K, \rho, K^*) Decays and Leptophobic Z^\prime Model
We consider the exclusive flavor changing neutral current processes B -> M
\nu \bar{\nu} (M= \pi, K, \rho, K^*) in the leptophobic Z^\prime model, in
which the charged leptons do not couple to the extra Z^\prime boson. We find
that these exclusive modes are very effective to constrain the leptophobic
Z^\prime model. In the leptophobic Z^\prime model, additional right-handed
neutrinos are introduced and they can contribute to the missing energy signal
in B -> M + E_missing decays. Through the explicit calculations, we obtain
quite stringent bounds on the model parameters, |U_{sb}^{Z^\prime}| \leq 0.29
and |U_{db}^{Z^\prime}| \leq 0.61, from the already existing experimental data.
We also briefly discuss an interesting subject of massive right-handed
neutrinos, which might be connected with the dark matter problem.Comment: 17 pages, 3 figures, minor corrections, version to appear in PL
Possible evidence for the breakdown of the CKM-paradigm of CP-violation
Using primarily experimental inputs for S(B -> psi Ks), Delta M_Bs, Delta
M_Bd, BR(B -> tau nu) and epsilon_K along with necessary inputs from the
lattice, we find that the measured value of sin(2 beta) is smaller than
expectations of the Standard Model by as much as 3.3 sigma, and also that the
measured value of the BR(B -> tau nu) seems to be less than the predicted value
by about 2.8 sigma. However, through a critical study we show that most likely
the dominant source of these deviations is in B_d(s) mixings and in sin(2 beta)
and less so in B -> tau nu, and also that the bulk of the problem persists even
if input from epsilon_K is not used. The fact that kaon mixing and epsilon_K
are not the dominant source of the deviation from the Standard Model has the
very important consequence that model independent considerations imply that the
scale of the relevant new CP-violating physics is below O(2 TeV), thus
suggesting that direct signals of the new particle(s) may well be accessible in
collider experiments at the LHC and perhaps even at the Tevatron.Comment: 6 pages, 8 figures. Added another fit and some more discussion
showing that BR(B->tau nu) comes out in good agreement with predictions of
the SM if the measured value of sin2beta is not used as an input. References
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Weak phases from topological-amplitude parametrization
We propose a parametrization for two-body nonleptonic meson decays, in
which the various topologies of amplitudes are counted in terms of powers of
the Wolfenstein parameter . The weak phases and the
amplitudes are determined by comparing this parametrization with available
measurements. It is possible to obtain the phase from the
data up to theoretical uncertainty of . The recently
measured branching ratio implies a large color-suppressed
or penguin amplitude, and that the extraction of the phase from the
data may suffer theoretical uncertainty more than the expected one
of .Comment: 11 pages, 4 figure
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