Failure of classical elasticity in auxetic foams

A recent derivation [P.H. Mott and C.M. Roland, Phys. Rev. B 80, 132104 (2009).] of the bounds on Poisson's ratio, v, for linearly elastic materials showed that the conventional lower limit, -1, is wrong, and that v cannot be less than 0.2 for classical elasticity to be valid. This is a significant result, since it is precisely for materials having small values of v that direct measurements are not feasible, so that v must be calculated from other elastic constants. Herein we measure directly Poisson's ratio for four materials, two for which the more restrictive bounds on v apply, and two having values below this limit of 0.2. We find that while the measured v for the former are equivalent to values calculated from the shear and tensile moduli, for two auxetic materials (v < 0), the equations of classical elasticity give inaccurate values of v. This is experimental corroboration that the correct lower limit on Poisson's ratio is 0.2 in order for classical elasticity to apply.Comment: 9 pages, 2 figure

Electronic Structure of Electron-doped Sm1.86Ce0.14CuO4: Strong `Pseudo-Gap' Effects, Nodeless Gap and Signatures of Short Range Order

Angle resolved photoemission (ARPES) data from the electron doped cuprate superconductor Sm$_{1.86}$Ce$_{0.14}$CuO$_4$ shows a much stronger pseudo-gap or "hot-spot" effect than that observed in other optimally doped $n$-type cuprates. Importantly, these effects are strong enough to drive the zone-diagonal states below the chemical potential, implying that d-wave superconductivity in this compound would be of a novel "nodeless" gap variety. The gross features of the Fermi surface topology and low energy electronic structure are found to be well described by reconstruction of bands by a $\sqrt{2}\times\sqrt{2}$ order. Comparison of the ARPES and optical data from the $same$ sample shows that the pseudo-gap energy observed in optical data is consistent with the inter-band transition energy of the model, allowing us to have a unified picture of pseudo-gap effects. However, the high energy electronic structure is found to be inconsistent with such a scenario. We show that a number of these model inconsistencies can be resolved by considering a short range ordering or inhomogeneous state.Comment: 5 pages, 4 figure

The Hamiltonian boundary term and quasi-local energy flux

The Hamiltonian for a gravitating region includes a boundary term which determines not only the quasi-local values but also, via the boundary variation principle, the boundary conditions. Using our covariant Hamiltonian formalism, we found four particular quasi-local energy-momentum boundary term expressions; each corresponds to a physically distinct and geometrically clear boundary condition. Here, from a consideration of the asymptotics, we show how a fundamental Hamiltonian identity naturally leads to the associated quasi-local energy flux expressions. For electromagnetism one of the four is distinguished: the only one which is gauge invariant; it gives the familiar energy density and Poynting flux. For Einstein's general relativity two different boundary condition choices correspond to quasi-local expressions which asymptotically give the ADM energy, the Trautman-Bondi energy and, moreover, an associated energy flux (both outgoing and incoming). Again there is a distinguished expression: the one which is covariant.Comment: 12 pages, no figures, revtex

Tarantula Toxins Interact with Voltage Sensors within Lipid Membranes

Voltage-activated ion channels are essential for electrical signaling, yet the mechanism of voltage sensing remains under intense investigation. The voltage-sensor paddle is a crucial structural motif in voltage-activated potassium (Kv) channels that has been proposed to move at the protein–lipid interface in response to changes in membrane voltage. Here we explore whether tarantula toxins like hanatoxin and SGTx1 inhibit Kv channels by interacting with paddle motifs within the membrane. We find that these toxins can partition into membranes under physiologically relevant conditions, but that the toxin–membrane interaction is not sufficient to inhibit Kv channels. From mutagenesis studies we identify regions of the toxin involved in binding to the paddle motif, and those important for interacting with membranes. Modification of membranes with sphingomyelinase D dramatically alters the stability of the toxin–channel complex, suggesting that tarantula toxins interact with paddle motifs within the membrane and that they are sensitive detectors of lipid–channel interactions

Changing ischaemic lesion patterns in adult moyamoya disease

OBJECTIVES: Ischaemic stroke is a frequent manifestation in patients with adult moyamoya disease (MMD), but the relationship between the lesion pattern and disease severity has rarely been investigated. METHODS: Data were collected on a consecutive series of 65 adult patients with MMD who visited our hospital between 1999 and 2006. Among them, 32 patients with first ever ischaemic stroke were included. The ischaemic lesions were categorised by location and compared as follows: (1) cortical versus subcortical involvement and (2) anterior (fronto-temporal) versus posterior (parieto-occipital) involvement. The lesions were also compared by disease severity, as determined by the extent of intracranial artery involvement (Suzuki's grading method) and by perfusion status visualised on single photon emission computed tomography (SPECT). RESULT: Disease severity was significantly greater in patients with cortical involvement than in those with subcortical involvement (Suzuki's grade 4.17 (0.72) vs 2.70 (0.73); p<0.001). Disease severity was also significantly greater in patients with posterior involvement than in those with anterior involvement (4.50 (0.53) vs 2.83 (0.76); p<0.001). In most of the patients (83.3%) the perfusion defect area shown on SPECT was larger than the ischaemic lesion area shown on MRI. CONCLUSIONS: Patients with advanced stage adult MMD tended to have ischaemic lesions involving the cortex and posterior part of the brain and the stroke mechanism in these patients was largely associated with haemodynamic compromise. Our results suggest that the lesion pattern of ischaemic stroke may change along with the extent of arterial involvement.This study was supported by a grant from the Korea Health 21 R&D Project, Ministry of Health and Welfare, Republic of Korea (A060263)

Deficiency of plasminogen activator inhibitor‐2 results in accelerated tumor growth

BackgroundUpregulation of the plasminogen activation system, including urokinase plasminogen activator (uPA), has been observed in many malignancies, suggesting that co‐opting the PA system is a common method by which tumor cells accomplish extracellular matrix proteolysis. PAI‐2, a serine protease inhibitor, produced from the SERPINB2 gene, inhibits circulating and extracellular matrix‐tethered uPA. Decreased SERPINB2 expression has been associated with increased tumor invasiveness and metastasis for several types of cancer. PAI‐2 deficiency has not been reported in humans and PAI‐2‐deficient (SerpinB2−/−) mice exhibit no apparent abnormalities.ObjectivesWe investigated the role of PAI‐2 deficiency on tumor growth and metastasis.MethodsTo explore the long‐term impact of PAI‐2 deficiency, a cohort of SerpinB2−/− mice were aged to >18 months, with spontaneous malignancies observed in 4/9 animals, all of apparently vascular origin. To further investigate the role of PAI‐2 deficiency in malignancy, SerpinB2−/− and wild‐type control mice were injected with either B16 melanoma or Lewis lung carcinoma tumor cells, with markedly accelerated tumor growth observed in SerpinB2−/− mice for both cell lines. To determine the relative contributions of PAI‐2 from hematopoietic or nonhematopoietically derived sources, bone marrow transplants between wild‐type C57BL/6J and SerpinB2−/− mice were performed.Results and ConclusionsOur results suggest that PAI‐2 deficiency increases susceptibility to spontaneous tumorigenesis in the mouse, and demonstrate that SerpinB2 expression derived from a nonhematopoietic compartment is a key host factor in the regulation of tumor growth in both the B16 melanoma and Lewis lung carcinoma models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163438/2/jth15054_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163438/1/jth15054.pd

2021 occultations and transits of Linus orbiting (22) Kalliope: I. Polygonal and `cliptracing' algorithm

The satellite Linus orbiting the main-belt asteroid (22) Kalliope exhibited occultation and transit events in late 2021. A photometric campaign was organized and observations were taken by the TRAPPIST-South, SPECULOOS-Artemis, OWL-Net, and BOAO telescopes, with the goal to constrain models of this system. Our dynamical model is complex, with multipoles (up to the order $\ell = 2$), internal tides, and external tides. The model was constrained by astrometry (spanning 2001--2021), occultations, adaptive-optics imaging, calibrated photometry, as well as relative photometry. Our photometric model was substantially improved. A new precise (${<}\,0.1\,{\rm mmag}$) light curve algorithm was implemented, based on polygon intersections, which are computed exactly -- by including partial eclipses and partial visibility of polygons. Moreover, we implemented a `cliptracing' algorithm, based again on polygon intersections, in which partial contributions to individual pixels are computed exactly. Both synthetic light curves and synthetic images are then very smooth. Based on our combined solution, we confirmed the size of Linus, $(28\pm 1)\,{\rm km}$. However, this solution exhibits some tension between the light curves and the PISCO speckle-interferometry dataset. In most solutions, Linus is darker than Kalliope, with the albedos $A_{\rm w} = 0.40$ vs. $0.44$. This is confirmed on deconvolved images. A~detailed revision of astrometric data allowed us to revise also the $J_2 \equiv -C_{20}$ value of Kalliope. Most importantly, a~homogeneous body is excluded. For a differentiated body, two solutions exist: low-oblateness ($C_{20} \simeq -0.12$), with a~spherical iron core, and alternatively, high-oblateness ($C_{20} \simeq -0.22$) with an elongated iron core. These correspond to the low- and high-energy collisions, respectively, studied by means of SPH simulations in our previous work.Comment: Astronomy and Astrophysics, accepte