Rigid Envelope Research Articles

Artificial potential incorporated adaptive fixed-time sliding mode control for target capture

With the increasing development of space missions, techniques for space non-cooperative target capture are evolving into new stage with higher control requirements under various working scenarios. Imitation Human Hand Capture is an effective rigid envelope capture method and could grasp non-cooperative targets without any cooperative feature points. In order to guarantee the safety and increase the success rate of IHHC, an adaptive fixed-time sliding mode frame based on IHHC is proposed, in which the Imitation Human Hand Capture governs the stable grasp and the sliding mode frame governs the control performance. In the proposed control frame, a fixed-time sliding mode control method is employed and the settling time can be adaptively tuned with the artificial potential function formulated according to the base-target distance and the envelope state of the arms. The proposed control frame is verified through Lyapunov function and simulation tests. The results demonstrate the effectiveness of the proposed control frame.

Patient-specific Monte Carlo-based organ dose estimates in spiral CT via optical 3D body scanning and adaptation of a voxelized phantom dataset: proof-of-principle

Objective. We present a method for personalized organ dose estimates obtained before the computed tomography (CT) exam, via 3D optical body scanning and Monte Carlo (MC) simulations. Approach. A voxelized phantom is derived by adapting a reference phantom to the body size and shape measured with a portable 3D optical scanner, which returns the 3D silhouette of the patient. This was used as an external rigid envelope for incorporating a tailored version of the internal body anatomy derived from a phantom dataset (National Cancer Institute, NIH, USA) matched for gender, age, weight, and height. The proof-of-principle was conducted on adult head phantoms. The Geant4 MC code provided estimates of the organ doses from 3D absorbed dose maps in the voxelized body phantom. Main results. We applied this approach for head CT scanning using an anthropomorphic voxelized head phantom derived from 3D optical scans of manikins. We compared the estimates of head organ doses with those provided by the NCICT 3.0 software (NCI, NIH, USA). Head organ doses differed up to 38% using the proposed personalized estimate and MC code, with respect to corresponding estimates calculated for the standard (non-personalized) reference head phantom. Preliminary application of the MC code to chest CT scans is shown. Real-time pre-exam personalized CT dosimetry is envisaged with adoption of a Graphics Processing Unit-based fast MC code. Significance. The developed procedure for personalized organ dose estimates before the CT exam, introduces a new approach for realistic description of size and shape of patients via voxelized phantoms specific for each patient.

Campylobacter jejuni Antimicrobial Resistance Profiles and Mechanisms Determined Using a Raman Spectroscopy-Based Metabolomic Approach.

Rapid identification of antimicrobial resistance (AMR) profiles and mechanisms is critical for clinical management and drug development. However, the current AMR detection approaches take up to 48 h to obtain a result. Here, we demonstrate a Raman spectroscopy-based metabolomic approach to rapidly determine the AMR profile of Campylobacter jejuni, a major cause of foodborne gastroenteritis worldwide. C. jejuni isolates with susceptible and resistant traits to ampicillin and tetracycline were subjected to different antibiotic concentrations for 5 h, followed by Raman spectral collection and chemometric analysis (i.e., second-derivative transformation analysis, hierarchical clustering analysis [HCA], and principal-component analysis [PCA]). The MICs obtained by Raman-2nd derivative transformation agreed with the reference agar dilution method for all isolates. The AMR profile of C. jejuni was accurately classified by Raman-HCA after treating bacteria with antibiotics at clinical susceptible and resistant breakpoints. According to PCA loading plots, susceptible and resistant strains showed different Raman metabolomic patterns for antibiotics. Ampicillin-resistant isolates had distinctive Raman signatures of peptidoglycan, which is related to cell wall synthesis. The ratio of saturated to unsaturated fatty acids in the lipid membrane layer of ampicillin-resistant isolates was higher than in susceptible ones, indicating more rigid envelope structure under ampicillin treatment. In comparison, tetracycline-resistant isolates exhibited prominent Raman spectral features associated with proteins and nucleic acids, demonstrating more active protein synthesis than susceptible strains with the presence of tetracycline. Taken together, Raman spectroscopy is a powerful metabolic fingerprinting technique for simultaneously revealing the AMR profiles and mechanisms of foodborne pathogens. IMPORTANCE Metabolism plays the central role in bacteria to mediate the early response against antibiotics and demonstrate antimicrobial resistance (AMR). Understanding the whole-cell metabolite profiles gives rise to a more complete AMR mechanism insight. In this study, we have applied Raman spectroscopy and chemometrics to achieve a rapid, accurate, and easy-to-operate investigation of bacterial AMR profiles and mechanisms. Raman spectroscopy reduced the analysis time by an order of magnitude to obtain the same results achieved through traditional culture-based antimicrobial susceptibility approaches. It offers great benefits as a high-throughput screening method in food chain surveillance and clinical diagnostics. Meanwhile, the AMR mechanisms toward two representative antibiotic classes, namely, ampicillin and tetracycline, were revealed by Raman spectroscopy at the metabolome level. This approach is based on bacterial phenotypic responses to antibiotics, providing information complementary to that obtained by conventional genetic methods such as genome sequencing. The knowledge obtained from Raman metabolomic data can be used in drug discovery and pathogen intervention.

Cholesterol-dependent membrane fusion induced by the gp41 membrane-proximal external region-transmembrane domain connection suggests a mechanism for broad HIV-1 neutralization.

The HIV-1 glycoprotein 41 promotes fusion of the viral membrane with that of the target cell. Structural, biochemical, and biophysical studies suggest that its membrane-proximal external region (MPER) may interact with the HIV-1 membrane and induce its disruption and/or deformation during the process. However, the high cholesterol content of the envelope (ca. 40 to 50 mol%) imparts high rigidity, thereby acting against lipid bilayer restructuring. Here, based on the outcome of vesicle stability assays, all-atom molecular dynamics simulations, and atomic force microscopy observations, we propose that the conserved sequence connecting the MPER with the N-terminal residues of the transmembrane domain (TMD) is involved in HIV-1 fusion. This junction would function by inducing phospholipid protrusion and acyl-chain splay in the cholesterol-enriched rigid envelope. Supporting the functional relevance of such a mechanism, membrane fusion was inhibited by the broadly neutralizing 4E10 antibody but not by a nonneutralizing variant with the CDR-H3 loop deleted. We conclude that the MPER-TMD junction embodies an envelope-disrupting C-terminal fusion peptide that can be targeted by broadly neutralizing antibodies. Fusion of the cholesterol-enriched viral envelope with the cell membrane marks the beginning of the infectious HIV-1 replicative cycle. Consequently, the Env glycoprotein-mediated fusion function constitutes an important clinical target for inhibitors and preventive vaccines. Antibodies 4E10 and 10E8 bind to one Env vulnerability site located at the gp41 membrane-proximal external region (MPER)-transmembrane domain (TMD) junction and block infection. These antibodies display broad viral neutralization, which underscores the conservation and functionality of the MPER-TMD region. In this work, we combined biochemical assays with molecular dynamics simulations and microscopy observations to characterize the unprecedented fusogenic activity of the MPER-TMD junction. The fact that such activity is dependent on cholesterol and inhibited by the broadly neutralizing 4E10 antibody emphasizes its physiological relevance. Discovery of this functional element adds to our understanding of the mechanisms underlying HIV-1 infection and its blocking by antibodies.

Destabilization of Highly Rigid Bilayers Enriched in Cholesterol by the Membrane-Proximal External Region of HIV-1 gp41

Current models for HIV fusion incorporate the induction of curvature stress and/or membrane defects by the membrane-proximal external region (MPER) of the envelope glycoprotein 41 subunit. The enrichment in aromatic residues predicts a highly favorable membrane-bound state for MPER, which would insert into the interface of the viral membrane external monolayer. However, the high levels of cholesterol found in the lipid envelope (Cholesterol-to-phospholipid mole ratio: ≈1) suggest that MPER insertion will be hampered in functional virions. Here, we have varied the membrane composition in order to test systematically bilayer area compressibility modulus (Ka) and monolayer spontaneous curvature (Ro) effects on binding and pore opening by MPER-derived peptides. In addition, we have assessed the degree of exposure to solvent, based on the reactivity to anti-MPER antibody. Finally, using grazing incidence X-ray diffraction (GIXD) and specular X-ray reflectivity (XR) we have studied the interactions of the MPER peptides with phospholipid monolayers containing low and high levels of Cholesterol. Our results support a role for MPER in destabilizing the highly rigid envelope, and suggest that the establishment of favorable MPER-cholesterol interactions may help overcoming the restrictions to the insertion process.

Invagination process induced by 2D desiccation of colloidal solutions

The drying process of a suspension of hard colloidal particles is investigated in a circular thin cell which ensures a two-dimensional radial drying. During solvent removal the concentration of particles accumulates to the liquid–gas interface and reaches the close packing concentration: a rigid skin forms. During the evaporation of water, the length of this rigid envelope keeps on decreasing till it stops shrinking. Then a buckling process occurs that leads to an inversion of the curvature. At this time and after a steady decrease, the envelope periphery starts to increase while its inner volume keeps decreasing. This deformation continues as the depressed region extends and invaginates inside the film. An experimental procedure coupling imaging of the skin formation and drying kinetics measurements provides a complete description of the successive mechanisms: drying process, formation of the rigid skin and invagination process.

The flows induced by a heated oscillating sphere

Time-averaged flows induced by oscillations of a heated (or cooled) solid sphere immersed in a liquid are investigated. The cases of an infinite surrounding liquid and the liquid placed into the spherical rigid envelope are considered. The gravity is absent. The interaction of thermovibrational flows and vibrational Schlichting flows is studied. New generalized equations are used for the description of thermovibrational convection. Analytical solutions have been obtained for small values of the governing parameters, under restriction of creeping flows, both in the case of infinite surrounding liquid and liquid placed into the rigid envelope. It has been found that the vibrational flow essentially depends on the layer thickness and can be rather complicated in the case of small thicknesses. At a fixed layer thickness, the creeping flow structure is defined by only one parameter, which is the ratio of vibrational Grashof number and Schlichting parameter. In the case of arbitrary values of the parameters, vibrational flows have been studied by a finite-difference method. The evolution of the finite-amplitude vibrational flow structure with the increase of the vibrational Grashof number has been investigated.

Cracks and dislocation arrays in heterogeneous media

The paper considers the anti-plane strain model of a crack or dislocation array that is centrally situated within a circular cylindrical inhomogeneity surrounded by an infinite body, the elastic shear moduli of the two regions having different and unrestricted values; the appropriate shear stress at the crack or dislocation array and the applied stress at infinity have uniform values. The discussion of this general problem is restricted to the case where the crack or dislocation array size is small compared with the cylinder radius, the condition for crack extension and the number of dislocations within an array then being determined. Special situations are, however, considered in detail and for a crack within a cylinder it is shown that a close correspondence exists between the solutions for the cases where the surrounding material is either a rigid envelope or free space. This correspondence is even valid when the crack size is large compared with the cylinder radius; hence by determining separately the condition for extension of a crack of unrestricted size within a circular cylinder surrounded by a rigid envelope, the corresponding condition is derived for the case where the surrounding material is free space.

On the nature of the critical diameter

The structure of the detonation front in liquid and gaseous explosives is considered. The reaction is assumed to be initiated at the sites of collisions of oblique waves with each other and with rigid envelope. When there is no envelope, the periphery inhomogeneities that collided before with the envelope cease to initiate the reaction, no new inhomogeneities appear at the boundary, and those formed adjacently meet no partners to collide with. This results in a successive diminishing of the detonation front. A process of this kind may stop detonation, provided no new detonation front develops within the compressed explosive behind the shock wave left by the terminated reaction. The new detonation wave would travel over the compressed explosive, overcoming the attenuating detonation front, and restoring detonation throughout the charge section. This process is repeated in cycles. The critical-charge diameter is that at which the attenuating detonation front will not be restored by the wave travelling over the compressed explosive. This would occur in the event the old detonation front succeeded in disappearing and the rarefied waves from the charge periphery to rarefy the compressed explosive before a new detonation wave is initiated. Calculation is made for nitromethane at 20°C and liquid TNT at 82°C. The critical diameters obtained, 14.3 and 62 mm, are close to the experimental values of 18 and 68 mm, respectively.

Resonances of Biological Cells at Sonic Frequencies

The rate at which Paramecium caudatum is destroyed in a sound field of fixed intensity increases markedly in the neighborhood of 1.2 kc/sec. Similar optimum destructive frequencies have been found for six other species of paramecium and for a blepharisma species. Although the shapes of these animals are too complex to treat on a theoretical basis, reasonable theories can be developed for spheres having radii equal to the average radius of the animal. One theory, based on the existence of a non-rigid membrane with interfacial tension, T, separating two incompressible liquids, gives T = ca. 3 dynes/cm, agreeing in order of magnitude with values found for other cells by very different methods. An alternate theory postulates a rigid envelope surrounding the cell giving coefficients of rigidity about 104 dynes/cm2; this is within the range of values of fibrin gels. Either type of vibration would be excited readily by cavitation. The formulas for these modes and their derivation will be discussed.

Study of Explosions

WHETHER anything physical and instructive about the atmosphere can be learnt from a study of purposely produced explosions, I am not sure. Ordinary explosives must waste much of their energy on the earth; and if atmospheric waves are wanted, it would seem better to explode a balloon filled with a detonating gas, say a mixture of hydrogen and oxygen, at a considerable height. Gas exploded without any rigid envelope, as in a soap-bubble, makes a tremendous noise, since the energy is wholly expended on the atmosphere.

Societies and Academies

PARIS. Academy of Sciences, October 3.—M. Léon Guignard in the chair.—J. Costantin: Alpine biology. The modifications of the fungus Pleurotus Eryngii produced by an Alpine climate.—A. Rateau: A new locking screw nut. The system described and figured is suitable only for special work in which the cost is not of first importance. It permits an adjustment of the screw to 1/240th of a turn, with an absolutely safe lock.—G. Giraud: Non-linear partial differential equations of the second order of the elliptical type.—M. Drouin: Contribution to a general study of unlimited algorithms.—O. Cahen: A new aerial float. The use of an evacuated rigid envelope (sheet aluminium on a wooden framework) is suggested in place of a non-rigid balloon filled with a light gas.—L. Rodes: Does the earth exercise an influence on the formation of sun-spots?—E. Perucca: The Volta effect in a vacuum and in highly rarefied gases. The couples studied included Zn|Hg, Cd|Hg, Bi|Hg, and Sb| Hg, the experiments with the Zn|Hg couple being given in detail. There would appear to be a Volta effect in the absence of a superficial gas layer, —0.17 volt for Zn/Hg. Water vapour exerts no special influence On the voltages, but the effect of oxygen, even when dry, is very marked.M. Curie: The action of the infrared rays on phosphorescence. According to a recent theory of Ives and Lukiesh, there should be a diminution in the intensity of the X-rays reflected from the no-face of a crystal of cubic blende when infra-red radiation is allowed to fall on the face of the crystal. The experiment has been made by the author, with a negative result.