105 research outputs found
Phonon Conductivity Metrics for Compact, Linked-Cage, Layered, and Filled-Cage Crystals, Using Ab Initio, Molecular Dynamics and Boltzmann Transport Treatments
Atomic-level thermal transport in compact, layered, linked-cage, and filled-cage
crystals is investigated using a multiscale approach,combines the ab initio calculation, molecular dynamics (MD), Boltzman transport equations (BTE), and the kinetic theory. These materials are of great interests in energy storage, transport, and conversion. The structural metrics of phonon conductivity of these crystals are then explored.
An atomic structure-based model is developed for the understanding the relation
ship between the atomic structure and phonon transport in compact crystals at high
temperatures. The elemental electronegativity, element mass, and the arrangement
of bonds are found to be the dominant factors to determine the phonon conductivity.
As an example of linked-cage crystals, the phonon conductivity of MOF-5 is investigate over a wide temperature range using MD simulations and the Green-Kubo method. The temperature dependence of the thermal conductivity of MOF-5 is found to be weak at high temperatures, which results from the suppression of the long-range acoustic phonon transport by the special linked-cage structure. The mean free path of the majority of phonons in MOF-5 is limited by the cage size.
The phonon and electron transport in layered Bi2Te3 structure are investigated using the first-principle calculations, MD, and BTE. Strong anisotropy has been found for both phonon and electron transport due to the special layered structure. Temperature dependence of the energy gap and appropriate
modelling of relaxation times are found to be important for the prediction of the electrical transport in the intrinsic regime. The scattering by the acoustic, optical, and polar-optical phonons are found to dominate the electron transport. For filled skutterudite structure, strong coupling between the filler and the host is found. The interatomic bonds of the host are significantly affected by the filler. It is shown that without changing the
interatomic potentials for the host, the filler itself can not result in a lower phonon
conductivity for the filled structure. It is also found that the behavior of partially-filled skutterudites can be better understood by treating the partially-filled structure
as a solid solution of the empty structure and fully-filled structure.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61561/1/baolingh_1.pd
Selective Solar Harvesting Windows for Full‐Spectrum Utilization
Smart windows can selectively regulate excess solar radiation to reduce heating and cooling energy consumption in the built environment. However, the inevitable dissipation of ultraviolet and near-infrared into waste heat results in inefficient solar utilization. Herein, a dual-band selective solar harvesting (SSH) window is developed to realize full-spectrum utilization. A transparent photovoltaic, converting ultraviolet into electricity, and a transparent solar absorber, converting near-infrared into thermal energy, are integrated and coupled with a ventilation system to extract heat for indoor use. Compared with common transparent photovoltaics, the SSH window increases solar harvesting efficiency up to threefold while maintaining a considerable visible transmittance. Simulations suggest that the SSH window, besides generating electricity, delivers energy savings by over 30% higher than common smart windows. This is the first integration of transparent photovoltaic and transparent solar absorber into a window, which may open up a new avenue for the development of energy-efficient buildings
Quartic Anharmonicity Triggers Conversion of Dominant Thermal Transport Channels in Lead-free Halide Double Perovskite Cs2AgBiBr6
We investigate the microscopic mechanisms of anharmonic lattice dynamics and
thermal transport in lead-free halide double perovskite Cs2AgBiBr6 from first
principles. We combine self-consistent phonon calculations with bubble diagram
correction and a unified theory of lattice thermal transport that considers
both the particle-like phonon propagation and wave-like tunnelling of phonons.
An ultra-low thermal conductivity at room temperature (~0.21 Wm-1K-1) is
predicted with weak temperature dependence(~T-0.45), in sharp contrast to the
conventional ~T-1 dependence. Particularly, the vibrational properties of
Cs2AgBiBr6 are featured by strong anharmonicity and wave-like tunnelling of
phonons. Anharmonic phonon renormalization from both the cubic and quartic
anharmonicities are found essential in precisely predicting the phase
transition temperature in Cs2AgBiBr6 while the negative phonon energy shifts
induced by cubic anharmonicity has a significant influence on particle-like
phonon propagation. Further, the contribution of the wave-like tunnelling to
the total thermal conductivity surpasses that of the particle-like propagation
above around 340 K, indicating the breakdown of the phonon gas picture
conventionally used in the Peierls-Boltzmann Transport Equation. Importantly,
when considering only three-phonon scatterings, the particle-like propagation
channel dominates the thermal transport in Cs2AgBiBr6. However, further
including four-phonon scatterings induced by quartic anharmonicity results in
the dominance of wave-like tunnelling. Our work highlights the importance of
lattice anharmonicity and wave-like tunnelling of phonons in the thermal
transport in lead-free halide double perovskites
Wave-like Tunneling of Phonons Dominates Glass-like Thermal Transport in Quasi-1D Copper Halide CsCu2I3
Fundamental understanding of thermal transport in compounds with ultra-low
thermal conductivity remains challenging, primarily due to the limitations of
conventional lattice dynamics and heat transport models. In this study, we
investigate the thermal transport in quasi-one-dimensional (1D) copper halide
CsCu2I3 by employing a combination of first principles-based self-consistent
phonon calculations and a dual-channel thermal transport model. Our results
show that the 0-K unstable soft modes, primarily dominated by Cs and I atoms in
CsCu2I3, can be an-harmonically stabilized at ~ 75 K. Furthermore, we predict
an ultra-low thermal conductivity of 0.362 Wm^(-1) K^(-1) along the chain axis
and 0.201 Wm^(-1) K^(-1) along cross chain direction in CsCu2I3 at 300 K.
Importantly, we find that an unexpected anomalous trend of increasing
cross-chain thermal conductivity with increasing temperature for CsCu2I3,
following a temperature dependence of ~T 0.106, which is atypical for a single
crystal and classified as an abnormal glass-like behavior. The peculiar
temperature-dependent behavior of thermal conductivity is elucidated by the
dominant wave-like tunnelling of phonons in thermal transport of CsCu2I3 along
cross-chain direction. In contrast, particle-like phonon propagation primarily
contributes to the chain-axis thermal conductivity across the entire
temperature range of 300-700 K. The sharp difference in the dominant thermal
transport channels between the two crystallographic directions can be
attributed to the unique chain-like quasi-1D structure of CsCu2I3. Our study
not only illustrates the microscopic mechanisms of thermal transport in CsCu2I3
but also paves the way for searching for and designing materials with ultra-low
thermal conductivity
Infrared anomalies in ultrathin Ti3C2Tx MXene films
Visible transparent but infrared reflective materials are ideal candidates
for both transparent conductive films and low-emissivity glass, which are
highly desired in a broad variety of areas such as touchscreens and displays,
photovoltaics, smart windows, and antistatic coatings. Ultrathin Ti3C2Tx MXene
films are emerging as promising low-emissivity transparent candidates. However,
the fundamental IR properties of Ti3C2Tx has not been revealed experimentally
due to daunting challenges in the preparation of continuous, large-area, and
ultrathin films of optical quality on flat substrates. Herein, we proposed a
tape-free transfer method that can help prepare centimeter-size and ultrathin
(down to 8 nm) Ti3C2Tx films on diverse optical substrates. Benefitting from
this method, the refractive index and permittivity for Ti3C2Tx were
successfully measured. Ti3C2Tx films exhibit large in-plane permittivity in the
IR region, yielding maximum IR reflectance of 88% for bulk films.
Interestingly, three anomalies were found in ultrathin Ti3C2Tx films: strong
dispersion in the permittivity, interlayer space-dependent optical properties,
and abnormally high IR absorption for a 15-nm-thick film. These anomalies are
important guidelines in the design of Ti3C2Tx-based low-emissivity transparent
films and other related devices, and may inspire other intriguing applications
such as ultrathin IR absorption coatings and tunable IR optical devices
Entomopathogenic Fungi on Hemiberlesia pitysophila
Hemiberlesia pitysophila Takagi is an extremely harmful exotic insect in forest to Pinus species, including Pinus massoniana. Using both morphological taxonomy and molecular phylogenetics, we identified 15 strains of entomogenous fungi, which belong to 9 genera with high diversities. Surprisingly, we found that five strains that were classified as species of Pestalotiopsis, which has been considered plant pathogens and endophytes, were the dominant entomopathogenic fungus of H. pitysophila. Molecular phylogenetic tree established by analyzing sequences of ribosomal DNA internal transcribed spacer showed that entomopathogenic Pestalotiopsis spp. were similar to plant Pestalotiopsis, but not to other pathogens and endophytes of its host plant P. massoniana. We were the first to isolate entomopathogenic Pestalotiopsis spp. from H. pitysophila. Our findings suggest a potential and promising method of H. pitysophila bio-control
Association Analysis of IL-17A and IL-17F Polymorphisms in Chinese Han Women with Breast Cancer
Background: Research into the etiology of breast cancer has recently focused on the role of the immunity and inflammation. The proinflammatory cytokines IL-17A and IL-17F can mediate inflammation and cancer. To evaluate the influences of IL-17A and IL-17F gene polymorphisms on the risk of sporadic breast cancer, a case-control study was conducted in Chinese Han women. Methodology and Principal Findings: We genotyped three single-nucleotide polymorphisms (SNPs) in IL-17A (rs2275913, rs3819025 and rs3748067) and five SNPs in IL-17F (rs7771511, rs9382084, rs12203582, rs1266828 and rs763780) to determine the haplotypes in 491 women with breast cancer and 502 healthy individuals. The genotypes were determined using the SNaPshot technique. The differences in the genotypic distribution between breast cancer patients and healthy controls were analyzed with the Chi-square test for trends. For rs2275913 in IL-17A, the frequency of the AA genotype was higher in patients than controls (P = 0.0016). The clinical features analysis demonstrated significant associations between IL-17 SNPs and tumor protein 53 (P53), progesterone receptor (PR), human epidermal growth factor receptor 2 (Her-2) and triple-negative (ER-/PR-/Her-2-) status. In addition, the haplotype analysis indicated that the frequency of the haplotype A rs2275913G rs3819025G rs3748067, located in the IL-17A linkage disequilibrium (LD) block, was higher in patients than in controls (P = 0.0471 after correction for multiple testing)
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