Temperature-dependent transport measurements with Arduino

The current performances of single-board microcontrollers render them attractive, not only for basic applications, but also for more elaborate projects, amongst which are physics teaching or research. In this article, we show how temperature-dependent transport measurements can be performed by using an Arduino board, from cryogenic temperatures up to room temperature or above. We focus on two of the main issues for this type of experiments: the determination of the sample temperature and the measurement of its resistance. We also detail two student-led experiments: evidencing the magnetocaloric effect in Gadolinium and measuring the resistive transition of a high critical temperature superconductor. Received: 7 July 2018,  Accepted: 27 September 2018; Edited by: A. Marti,  M. Monteiro;  Reviewed by: R. Marotti, Instituto de Física, Facultad de Ingeniería - Universidad de la República, Uruguay; DOI: http://dx.doi.org/10.4279/PIP.100007 Cite as: A Hilberer, G Laurent, A Lorin, A Partier, J Bobroff, F Bouquet, C Even, J M Fischbach, C A Marrache Kikuchi, M Monteverde, B Pilette, Q Quay,  Papers in Physics 10, 100007(2018) This paper, by A Hilberer, G Laurent, A Lorin, A Partier, J Bobroff, F Bouquet, C Even, J M Fischbach, C A Marrache Kikuchi, M Monteverde, B Pilette, Q Quay, is licensed under the Creative Commons Attribution License 4.0.    

Lipid-destabilising properties of a peptide with structural plasticity

The Chameleon peptide (Cham) is a peptide designed from two regions of the GB1 protein, one folded as an alpha-helix and the other as a beta structure. Depending on the environment, the Cham peptide adopts an alpha or a beta conformation when inserted in different locations of GB1. This environment dependence is also observed for tilted peptides. These short protein fragments, able to destabilise organised system, are mainly folded in beta structure in water and in alpha helix in a hydrophobic environment, like the lipid bilayer. In this paper, we tested whether the Cham peptide can be qualified as a tilted peptide. For this, we have compared the properties of Cham peptide (hydrophobicity, destabilising properties, conformation) to those of tilted peptides. The results suggest that Cham is a tilted peptide. Our study, together the presence of tilted fragments in transconformational proteins, suggests a relationship between tilted peptides and structural lability.

The N-terminal 12 Residue Long Peptide of HIV gp41 is the Minimal Peptide Sufficient to Induce Significant T-cell-like Membrane Destabilization in Vitro

Here, we predicted the minimal N-terminal fragment of gp41 required to induce significant membrane destabilization using IMPALA. This algorithm is dedicated to predict peptide interaction with a membrane. We based our prediction of the minimal fusion peptide on the tilted peptide theory. This theory proposes that some protein fragments having a peculiar distribution of hydrophobicity adopt a tilted orientation at a hydrophobic/hydrophilic interface. As a result of this orientation, tilted peptides should disrupt the interface. We analysed in silico the membrane-interacting properties of gp41 N-terminal peptides of different length derived from the isolate BRU and from an alignment of 710 HIV strains available on the Los Alamos National Laboratory. Molecular modelling results indicated that the 12 residue long peptide should be the minimal fusion peptide. We then assayed lipid-mixing and leakage of T-cell-like liposomes with N-terminal peptides of different length as first challenge of our predictions. Experimental results confirmed that the 12 residue long peptide is necessary and sufficient to induce membrane destabilization to the same extent as the 23 residue long fusion peptide. In silico analysis of some fusion-incompetent mutants presented in the literature further revealed that they cannot insert into a modelled membrane correctly tilted. According to this work, the tilted peptide model appears to explain at least partly the membrane destabilization properties of HIV fusion peptide.

All-optical induction of noncentrosymmetry in a transparent nonlinear polymer rod

What is believed to be the first evidence of an all-optical orientation of a highly transparent polymer is presented. The samples are bulk rods of poly(methyl methacrylate) grafted with paranitroaniline (PNA) obtained by use of copolymerization of methyl methacrylate (MMA) monomers mixed with grafted MMA-PNA monomers. Bulk samples were obtained after molding and polishing of the copolymer with standard techniques. Experiments show that the photoinduced second-order(1) susceptibility chi((2)) may occur through molecular reorientation following selective polar excitation of the nonlinear chromophores by simultaneous two- and three-photon absorption on the same electronic level.

Antenatal finding of intestinal obstruction caused by isolated segmental jejunal dilatation: a case report

The authors report a case of segmental jejunal dilatation that was discovered antenatally and manifested clinically as lower obstruction in a newborn boy. The antenatal ultrasound findings at 29, 30, and 31 weeks' gestation showed a constant hypoechogenic image (6 x 3 cm in diameter) localized to the right flank of the fetal abdomen, thought to be situated in the right colon. A prenatal diagnosis of incomplete right colonic stenosis was considered. In the immediate postnatal period, there were clinical manifestations of intestinal obstruction; however, results of a contrast enema and rectal biopsies were normal. An upper gastrointestinal contrast study showed a dilated jejunal loop situated approximately 15 cm from the ligament of Treitz. During surgery, a large dilated jejunal loop (7 cm in diameter, 15 cm in length) was found and resected. Histopathologic examination confirmed the diagnosis of segmental jejunal dilatation. This is the first antenatal illustration of this rare pathology, and it supports the hypothesis of a congenital origin for this anomaly.