Alcohol use disorders (AUDs) frequently co-occur with negative mood disorders, such as anxiety and depression, exacerbating relapse through dopaminergic dysfunction. Stress-related neuropeptides play ...a crucial role in AUD pathophysiology by modulating dopamine (DA) function. The rostromedial tegmental nucleus (RMTg), which inhibits midbrain dopamine neurons and signals aversion, has been shown to increase ethanol consumption and negative emotional states during abstinence. Despite some stress-related neuropeptides acting through the RMTg to affect addiction behaviors, their specific roles in alcohol-induced contexts remain underexplored. This study utilized an intermittent voluntary drinking model in mice to induce negative effect behavior 24 h into ethanol (EtOH) abstinence (post-EtOH). It examined changes in pro-stress (
,
,
) and anti-stress (
,
,
,
,
) neuropeptide-coding genes and analyzed their correlations with aversive behaviors. We observed that adult male C57BL/6J mice displayed evident anxiety, anhedonia, and depression-like symptoms at 24 h post-EtOH. The laser-capture microdissection technique, coupled with or without retrograde tracing, was used to harvest total ventral tegmental area (VTA)-projecting neurons or the intact RMTg area. The findings revealed that post-EtOH consistently reduced
and
levels while elevating
levels in these neuronal populations. Notably, RMTg
and
levels counteracted ethanol consumption and depression severity, while
levels were indicative of the mice's anxiety levels. Together, these results underscore the potential role of stress-related neuropeptides in the RMTg in regulating the negative emotions related to AUDs, offering novel insights for future research.
The effects of chirality and boundary conditions on the elastic properties and buckling behavior of single-walled carbon nanotubes are investigated using atomistic simulations. The influences of the ...tube length and diameter are also included. It is found that the elastic properties of carbon nanotubes at small deformations are insensitive to the tube chirality and boundary conditions during compression. However, for large deformations occurred upon both compression and bending, the tube buckling behavior is shown to be very sensitive to both tube chirality and boundary conditions. Therefore, while the popular continuum thin shell model can be successfully applied to describe nanotube elastic properties at small deformation such as the Young’s modulus, it cannot correctly account for the buckling behavior. These results may allow better evaluation of nanotube mechanical properties via appropriate atomistic simulations.
Raman spectroscopy is a new technique to properly measure the strain of two dimensional (2D) materials, based upon which a new characterizing approach for the elastic moduli of graphene membranes was ...proposed from the central strain of the bulged membrane under a given pressure measured via Raman spectroscopy. In the present work, using finite element modeling (FEM), it is found that the aforementioned approach cannot properly determine the elastic moduli of free standing 2D materials. The reasons are that the membranes measured in the bulge test are not pre-strain free, and that the central strain measured via Raman spectroscopy includes both the pre-strain and the strain induced by the applied pressure. From FEM results, the negative apparent pre-strain in the membranes (corresponding the slack membranes) can result in the overestimation of their elastic moduli. The present results can be further validated by the reported experimental results, in which the measured elastic moduli of graphene membranes were significantly overestimated. Effectively estimating the apparent pre-strain is the necessary condition to properly determine the elastic moduli of graphene membranes via the central strain measured via Raman spectroscopy.
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•A new bulge testing model is proposed for the membranes, including not only the flat and pre-stretched membranes (with ε0 ≥ 0) but also the slack membranes (with ε0 < 0), which relates the membrane ...central strain and the applied pressure;.•Based upon the new proposed model, an innovative approach to characterize the elastic moduli of freestanding 2D materials can be established;.•An innovative characterizing approach for e is much simpler and less sensitive to the measurement uncertainty than the conventional bulge testing;.•With the present model, the new experimental technique, Raman spectroscopy, can be used to characterize the elastic moduli of 2D materials;.•With the present model, similar as indentation technique, the bulge testing can be also a standard technique to characterize the elastic moduli of 2D materials;.•Using FEM, we found that in pressure bulge testing, the stretching of the freestanding graphene under the adhesive boundary condition is same as that of the slack membrane with the apparent pre-strain ε0 = e0-s/a;.•The effectiveness of the new proposed model and approach can be validated by FEM results given in the present work and the reported experimental results.
Freestanding 2D materials are essentially under the adhesive boundary condition instead of the typically assumed clamped boundary condition, and the membrane deformation in pressure bulge testing is actually similar as that of the slack membrane. A new bulge testing model of freestanding 2D materials is proposed from the central strain of the bulged membrane under a given pressure, based upon which the elastic moduli of 2D materials can be properly characterized by an easy testing approach. In this approach, instead of using a complex pressure loading and measuring system, the 2D materials mounted on the substrate with circular holes are simply placed into the vacuum chamber, and the moduli of materials can be characterized from their central strain measured via Raman spectroscopy. In addition, finite element modeling (FEM) is employed to validate the effectiveness of the model proposed in the present work. The present approach can provide a useful guideline on effectively characterizing the elastic moduli of 2D materials via a very simple approach, based upon which the elastic moduli can be characterized via a new technique, like Raman spectroscopy.
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The tensile properties of graphene with the Stone-Wales (S–W) defect are investigated by first principle calculations. It is found that the defect will not affect the elastic modulus and Poisson's ...ratio of graphene but causes the pre-stress of graphene, which makes the graphene to be anisotropic: the deformation along one direction is much easier than that along another direction. The pre-stress field causes only about 10% decrease of the intrinsic stress of graphene but causes more than 50% decrease of the maximum failure strain, which is significantly different with the results calculated by the empirical potential. The main reason is that the pre-stress field created by the S–W defect predicted by first principle calculations is different than that calculated from molecular mechanics simulations. In addition, it is also found that the theoretical solution (on the basis of the continuum disclination dipoles model) of the pre-stress field created by the S–W defect is also different with that determined from MM simulations, which is different from the results of the aligned 7-5 defects of graphene.
Free-standing (FS) two-dimensional (2D) materials are commonly found under an adhesive boundary condition, i.e., a small portion near the boundary is adhered to the sidewall of a cylindrical hole in ...a substrate via van der Waals (vdW) interaction, but its influence on mechanical properties characterization via indentation testing has never been considered. Based on the analyses of both experimental and numerical results, we found that the separation of the adhesive boundary of monolayer graphene prepared by chemical vapor deposition (CVD) in indentation tests is indeed possible. The adhesive boundary effect on indentation response can be clearly shown from indentation loading -reloading curves, including a nominal material softening in the first loading response and a nominal material stiffening in the consecutive reloading responses, caused by the coupling effect of the vdW interactions with an AFM tip and with a substrate near the boundary of the FS region. Thus, the conventional assumption of a clamped boundary in the existing FS indentation models is inappropriate. Finally, a tentative approach to eliminate the adhesive boundary effect on the indentation response is suggested, in which the intrinsic property of a CVD grown graphene might be obtained via a large AFM tip after several loading-unloading-reloading cycles.
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Based upon the homogeneous skull model, the skull/brain assembly can be simplified as a homogeneous-shell (HMS)/core structure, in which the exterior shell and interior core represent the skull and ...brain, respectively. From the blast responses of the spherical shell/core structures calculated
finite element modeling, it is found that the existing homogeneous skull model developed by the well-accepted approach based upon three-point bending tests cannot properly describe the blast response of the skull, modeled as a three-layered sandwich (TLS) shell in the present work, e.g. the average error in the calculated core (brain) pressure is up to ∼30%. Moreover, an innovative approach based upon inverse analysis procedure is then proposed to develop a modified homogeneous skull model, which can give a proper description of the blast response of the skull (a TLS shell), e.g. the average error in the calculated core (brain) pressure is reduced to ∼7%. It is concluded that the well-accepted three-point bending approach cannot develop an effective HMS skull model for studying the blast response of the skull/brain assembly, upon which the model parameter will be overestimated by ∼60%; instead, the innovative approach based upon inverse analysis procedure should be adopted.
•A paradox is commonly found in indentation testing of multiple layer 2D materials: the measured indentation load-displacement curve has a much longer linear stage than the corresponding theoretical ...counterpart; in addition, the elastic modulus determined is significantly lower than its theoretical counterpart. Based on the theoretical and numerical analyses, the above paradox can be well explained via the separation of the adhesive boundary of 2D materials in indentation tests, resulting in that the FS portion of sample behaves like a pure bending beam/plate, instead of a doubly clamped beam/plated subject to a central point load. These results agree with the reported experimental results very well, and thus, the indentation response of multiple layer 2D materials should be analyzed via the pure bending model instead of the classical indentation bending model of beam/plate.
Elastic modulus of multiple layer two-dimensional (2D) materials is typically measured in indentation testing via existing indentation bending model of a beam/plate, in which the sample is assumed to be a doubly clamped beam/plate under a central point load. However, a paradox is commonly found in indentation testing of multiple layer 2D materials: the measured indentation load-displacement curve has a much longer linear regime than the corresponding theoretical counterpart; in addition, the elastic modulus determined is significantly lower than its theoretical counterpart. Based on the theoretical and numerical analyses, the above paradox can be well explained via the separation of the adhesive boundary of 2D materials in indentation tests, resulting in that the freestanding portion of sample behaves like a pure bending beam/plate, instead of a doubly clamped beam/plate subjected to a central point load. These results agree with the reported experimental results very well, and thus, the indentation response of multiple layer 2D materials should be analyzed via the pure bending model instead of the existing indentation bending model of beam/plate.
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It is of fundamental value to understand the thermo-mechanical properties of carbon nanotubes. In this paper, by using molecular dynamics simulation, a systematic numerical investigation is carried ...out to explore the natural thermal vibration behaviors of single-walled carbon nanotubes and their quantitative contributions to the apparent thermal contraction behaviors. It is found that the thermo-mechanical behavior of single-walled carbon nanotubes is exhibited through the competition between quasi-static thermal expansion and dynamic thermal vibration, while the vibration effect is more prominent and induces apparent contraction in both radial and axial directions. With increasing temperature, the anharmonic interatomic potential helps to increase the bond length, which leads to thermally induced expansion. On the other hand, the higher structural entropy and vibrational entropy of the system cause the carbon nanotube to vibrate, and the apparent length of nanotube decreases due to various vibration modes. Parallel analytical and finite element analyses are used to validate the vibration frequencies and provide helpful insights. The unified multi-scale study has successfully decoupled and systematically analyzed both thermal expansion and contraction behaviors of single-walled carbon nanotube from 100 to 800
K, and obtained detailed information on various vibration modes as well as their quantitative contributions to the coefficient of thermal expansion in axial and radial directions. The results of this paper may provide useful information on the thermo-mechanical integrity of single-walled carbon nanotubes, and become important in practical applications involving finite temperature.
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