f(Q, T) gravity Xu, Yixin; Li, Guangjie; Harko, Tiberiu ...
The European physical journal. C, Particles and fields,
08/2019, Letnik:
79, Številka:
8
Journal Article
Recenzirano
Odprti dostop
We propose an extension of the symmetric teleparallel gravity, in which the gravitational action
L
is given by an arbitrary function
f
of the non-metricity
Q
and of the trace of the ...matter-energy-momentum tensor
T
, so that
L
=
f
(
Q
,
T
)
. The field equations of the theory are obtained by varying the gravitational action with respect to both metric and connection. The covariant divergence of the field equations is obtained, with the geometry–matter coupling leading to the nonconservation of the energy-momentum tensor. We investigate the cosmological implications of the theory, and we obtain the cosmological evolution equations for a flat, homogeneous and isotropic geometry, which generalize the Friedmann equations of general relativity. We consider several cosmological models by imposing some simple functional forms of the function
f
(
Q
,
T
), corresponding to additive expressions of
f
(
Q
,
T
) of the form
f
(
Q
,
T
)
=
α
Q
+
β
T
,
f
(
Q
,
T
)
=
α
Q
n
+
1
+
β
T
, and
f
(
Q
,
T
)
=
-
α
Q
-
β
T
2
. The Hubble function, the deceleration parameter, and the matter-energy density are obtained as a function of the redshift by using analytical and numerical techniques. For all considered cases the Universe experiences an accelerating expansion, ending with a de Sitter type evolution. The theoretical predictions are also compared with the results of the standard
Λ
CDM model.
We consider an
f
(
Q
,
T
) type gravity model in which the scalar non-metricity
Q
α
μ
ν
of the space-time is expressed in its standard Weyl form, and it is fully determined by a vector field
w
μ
. ...The field equations of the theory are obtained under the assumption of the vanishing of the total scalar curvature, a condition which is added into the gravitational action via a Lagrange multiplier. The gravitational field equations are obtained from a variational principle, and they explicitly depend on the scalar nonmetricity and on the Lagrange multiplier. The covariant divergence of the matter energy-momentum tensor is also determined, and it follows that the nonmetricity-matter coupling leads to the nonconservation of the energy and momentum. The energy and momentum balance equations are explicitly calculated, and the expressions of the energy source term and of the extra force are found. We investigate the cosmological implications of the theory, and we obtain the cosmological evolution equations for a flat, homogeneous and isotropic geometry, which generalize the Friedmann equations of standard general relativity. We consider several cosmological models by imposing some simple functional forms of the function
f
(
Q
,
T
), and we compare the predictions of the theory with the standard
Λ
CDM model.
•The thermal conductance across Si/4H-SiC is modulated broadly from ∼300 to ∼1000 MW/m2K via confining nanopatterns in the interfacial region.•The thermal conductance across Si/4H-SiC interface shows ...a nonmonotonic nanopattern section dependence.•The thermal conductance is enhanced by ∼11% compared to that of the bare Si/4H-SiC interface once the enhance of the phonon channels is dominant.
Manipulating the thermal transport across the interfaces via nanostructuring is critical for thermal management in electronics and energy conversion in thermoelectrics. Recent experiments have enabled the fabrication of controllable nanopatterns at interfaces, and therefore provide a new perspective to design and manipulate interfacial heat transfer. By performing nonequilibrium molecular dynamics simulations, we reported that the interfacial thermal conductance of Si/4H-SiC interfaces can be modulated broadly from ∼ 300 MW/m2K to ∼ 1000 MW/m2K by confining nanopatterns with a thickness on the order of nanometers, i.e., smaller than 30 nm. Based on the spectral heat current and participation ratio analysis, the nonmonotonic nanopattern section-dependent thermal conductance as observed in our simulations was found to be originated from two competing mechanisms, i.e., phonon-boundary scattering and interfacial phonon transport channels. The corresponding interfacial thermal conductance initially decreased with the nanopattern section when the phonon-boundary scattering is dominant and became stronger, and then increased when there were many more possible interfacial phonons transport channels. The thermal conductance was enhanced by ∼11% compared to that of the bare Si/4H-SiC interface once the latter mechanism was dominant. Besides, the thermal resistance induced by the pattern itself becomes evident and must be considered when the height of the nanopattern becomes greater. Our work here provides a comprehensive investigation on manipulating the thermal transport across the interfaces via controllable nanopatterns, which is important and meaningful for designing and optimizing the advanced thermal interface materials.
Background. Adenosine, derived from the degradation of ATP via ectonucleotidases CD39 and CD73, is a critical immunosuppressive metabolite in the hypoxic microenvironment of tumor tissue. Adenosine ...signaling via A2aR can inhibit the antitumor immune response of CD8+ T cells. CD39 and CD73 high-expressing Tregs play a critical role in tumor immune evasion of gastric cancer (GC). The present study investigated the underlying mechanism by which Tregs suppress antitumor immune responses in GC. Materials and Methods. Fifty-two GC samples were collected, and the frequency of FoxP3+ Tregs and CD8+ T cells and density ratios of A2aR+/CD8+ T cells, CD39+/FoxP3+ Tregs, and CD73+/FoxP3+ Tregs in GC were assessed with multiplex immunofluorescence. The expression of FoxP3 and A2aR in GC tissues was also detected by the immunoblotting assay. We next investigated the relationship between density of FoxP3+ Tregs, ratio of A2aR+/CD8+ T cells, and clinicopathological parameters. At the same time, Tregs and CD8+ T cells were isolated from peripheral blood of five GC patients, and the antagonists of CD39 and CD73 were used to assess the ability of Tregs to decompose ATP into adenosine. In addition, we cocultured CD8+ T cells and Tregs with antagonists of A2aR and A2bR in order to examine the alterations in immune function of CD8+ T cells. Results. The density of both FoxP3+ Tregs and A2aR+/CD8+ T cells was higher in GC tissue compared to peritumoral normal tissue and significantly correlated with the TNM stage, lymph node metastasis, and distant metastasis of GC. The process of Treg hydrolysis of ATP into adenosine was blocked by the antagonists of CD39 and CD73. In addition, Tregs could induce apoptosis and inhibit proliferation of CD8+ T cells, while this effect could be obviously reduced by applying the antagonist of A2aR or A2aR+A2bR. Moreover, IFN-γ, TNF-α, and perforin generated by CD8+ T cells could also be inhibited through the adenosine A2aR pathway. Conclusions. The FoxP3+ Tregs and A2aR+/CD8+ T cells were excessively infiltrated in GC tissue. Tregs from GC can decompose ATP to adenosine and in turn induce apoptosis and inhibit the proliferation of CD8+ T cells through the A2aR pathway, further leading to immune escape of GC.
Three-dimensional graphene network is a promising structure for improving both the mechanical properties and functional capabilities of reinforced polymer and ceramic matrix composites. However, ...direct application in a metal matrix remains difficult due to the reason that wetting is usually unfavorable in the carbon/metal system. Here we report a powder-metallurgy based strategy to construct a three-dimensional continuous graphene network architecture in a copper matrix through thermal-stress-induced welding between graphene-like nanosheets grown on the surface of copper powders. The interpenetrating structural feature of the as-obtained composites not only promotes the interfacial shear stress to a high level and thus results in significantly enhanced load transfer strengthening and crack-bridging toughening simultaneously, but also constructs additional three-dimensional hyperchannels for electrical and thermal conductivity. Our approach offers a general way for manufacturing metal matrix composites with high overall performance.
Time-varying effects simulation plays a critical role in computer graphics. Fruit diseases are typical time-varying phenomena. Due to the biological complexity, the existing methods fail to represent ...the biodiversity and biological law of symptoms. To this end, this paper proposes a biology-aware, physically-based framework that respects biological knowledge for realistic simulation of fruit mildew diseases. The simulated symptoms include skin discoloration, fungus growth, and volume shrinkage. Specifically, we take advantage of both the zero-order kinetic model and reaction–diffusion model to represent the complex fruit skin discoloration related to skin biological characteristics. To reproduce 3D mildew growth, we employ the Poisson-disk sampling technique and propose a template model instancing method. One can flexibly change hyphal template models to characterize the fungal biological diversity. To model the fruit’s biological structure, we fill the fruit mesh interior with particles in a biologically-based arrangement. Based on this structure, we propose a turgor pressure and a Lennard-Jones force-based adaptive mass–spring system to simulate the fruit shrinkage in a biological manner. Experiments verified that the proposed framework can effectively simulate mildew diseases, including gray mold, powdery mildew, and downy mildew. Our results are visually compelling and close to the ground truth. Both quantitative and qualitative experiments validated the proposed method.
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One critical issue to phosphoric acid (PA) doped high-temperature proton exchange membranes (HT-PEMs) is to balance the proton conductivity and mechanical properties for overall application ...performance in fuel cells. Addressing the issue, we prepare durable HT-PEMs having the dual crosslinking structure by employing poly(vinylimidazole-divinylbenzene-styrene) (poly(VIm-DVB-St)) copolymer as a crosslinker and using the poly (aromatic ether ketone) (PAEK) polymer containing four methyl groups as the host membrane matrix. The imidazole groups of poly(VIm-DVB-St) react with benzyl bromide groups of brominated PAEK for both the primary cross-linking network and high PA doping. The divinylbenzene crosslinked poly (styrene-co-vinylimidazole) network generates the secondary cross-linking structure. The formed reticular polymer chain structure brings on low swelling and high mechanical strength of the HT-PEMs. The fuel cell based on the acid doped PAEK41-85%VIm/233.0 PA shows a H2-air fuel cell peak power density of 306 mW cm−2 at 200 °C without back pressure, and a low degradation rate of 3.9 × 10−5 V h−1 during a period of 600 h under a constant current density of 200 mA cm−2 at 160 °C.
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•Construction of dual cross-linked structure of HT-PEMs for superior properties.•High proton conductivity and mechanical strength of the prepared membranes.•The membrane-based single fuel cell (H2/air) operates stably at 160 °C for 600 h.
Accumulating studies have revealed that aberrant expression of circular RNAs (circRNAs) is widely involved in the tumorigenesis and progression of malignant cancers, including colorectal cancer ...(CRC). Nevertheless, the clinical significance, levels, features, biological function, and molecular mechanisms of novel circRNAs in CRC remain largely unexplored.
CRC-related circRNAs were identified through bioinformatics analysis and verified in clinical specimens by qRT-PCR and in situ hybridization (ISH). Then, in vitro and in vivo experiments were performed to determine the clinical significance of, functional roles of, and clinical characteristics associated with circIL4R in CRC specimens and cells. Mechanistically, RNA pull-down, fluorescence in situ hybridization (FISH), luciferase reporter, and ubiquitination assays were performed to confirm the underlying mechanism of circIL4R.
CircIL4R was upregulated in CRC cell lines and in sera and tissues from CRC patients and was positively correlated with advanced clinicopathological features and poor prognosis. Functional experiments demonstrated that circIL4R promotes CRC cell proliferation, migration, and invasion via the PI3K/AKT signaling pathway. Mechanistically, circIL4R was regulated by TFAP2C and competitively interacted with miR-761 to enhance the expression of TRIM29, thereby targeting PHLPP1 for ubiquitin-mediated degradation to activate the PI3K/AKT signaling pathway and consequently facilitate CRC progression.
Our findings demonstrate that upregulation of circIL4R plays an oncogenic role in CRC progression and may serve as a promising diagnostic and prognostic biomarker for CRC detection and as a potential therapeutic target for CRC treatment.
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