抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

We measured the elastic properties and intrinsic breaking strength of free-standing monolayer graphene membranes by nanoindentation in an atomic force microscope. The force-displacement behavior is interpreted within a framework of nonlinear elastic stress-strain response, and yields second- and third-order elastic stiffnesses of 340 newtons per meter (N m(-1)) and -690 Nm(-1), respectively. The breaking strength is 42 N m(-1) and represents the intrinsic strength of a defect-free sheet. These quantities correspond to a Young's modulus of E = 1.0 terapascals, third-order elastic stiffness of D = -2.0 terapascals, and intrinsic strength of sigma(int) = 130 gigapascals for bulk graphite. These experiments establish graphene as the strongest material ever measured, and show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime.

/pdf/measurement-of-the-elastic-properties-and-intrinsic-strength-27nythtm75.pdf

Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene

Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

/pdf/electronics-and-optoelectronics-of-two-dimensional-2jbqr1unvw.pdf

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

We report the measurement of the thermal conductivity of a suspended single-layer graphene. The room temperature values of the thermal conductivity in the range ∼(4.84 ± 0.44) × 103 to (5.30 ± 0.48) × 103 W/mK were extracted for a single-layer graphene from the dependence of the Raman G peak frequency on the excitation laser power and independently measured G peak temperature coefficient. The extremely high value of the thermal conductivity suggests that graphene can outperform carbon nanotubes in heat conduction. The superb thermal conduction property of graphene is beneficial for the proposed electronic applications and establishes graphene as an excellent material for thermal management.

/pdf/superior-thermal-conductivity-of-single-layer-graphene-2op5i6aw2y.pdf

Superior Thermal Conductivity of Single-Layer Graphene

Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

http://science.sciencemag.org/content/sci/297/5582/787.full.pdf

Carbon Nanotubes--the Route Toward Applications

It is well known that noble gases are relatively inert which justifies their use as pressure-transmitting medium (PTM) in highpressure (HP) studies. Recent reports [1] indicate that various noble gases taken as PTM apparently influence the outcome of structural transformations. We reach the same conclusion by a systematic study of the structural changes of methyl-ammonium lead iodide, CH3NH3PbI3 (MAPbI3), a photovoltaic perovskite [2] with pressure by choosing Ne and Ar as two PTMs. The single crystal XRD experiments were performed using synchrotron radiation at room temperature up to 20 GPa. The crystal structure of MAPbI3 consists of a framework of corner-sharing PbI6 octahedra and methyl-ammonium cations, CH3NH3+ (MA), which is rotating in the cuboctahedral surrounding of twelve I-atoms. Weak hydrogen bonds statistically appeared between MA and I atoms give a high flexibility to the structure, which depends, in particular, on temperature and pressure. The large structural interstices offer the possibility to host other molecules which can alter the hydrogen bonds and destabilise the structure (see e.g., the case of water molecules [3]). We found the following structural consequences of the incorporation of Ne and Ar PTM into the interstices at HP. (i) The first-order phase transition from the tetragonal phase at ambient pressure (unit cell parameters a ≈ 8.8 Å, c ≈ 12.7 Å) to the (pseudo)cubic HP-phase (unit cell parameter a ≈ 12.3 Å) starts at pressures of about 1 and 0.1 GPa for Ar and Ne PTM, respectively. (ii) Above these pressures, a phase amorphization starts at about 1.5 GPa for Ar and 4 GPa for Ne. It is documented that a crystal of poor quality (high patchiness, inter-domain disorientation) is irreversibly amorphized, while a higher quality single crystal preserves partially a crystalline state up to 20 GPa for Ne-PTM. (iii) Ne-PTM series shows the pressure dependent incorporation of Ne and the loss of MA (see a graphic illustration). The transformation of the crystal composition can be expressed as: MAPbI3→Ne(x).MAPbI3→Ne(x).MA(1y).H(y)PbI3→Ne(x).HPbI3. The decompressed crystal shows NeMAPbI3 composition even after four weeks upon the decompression. Ar is assimilated by the structure to form Ar1.4MAPbI3 at 2.4 GPa and a complete, irreversible amorphisation follows at about 3.5 GPa. The difference between Ne and Ar used PTM is related to the difference in their atomic radii (0.38 and 0.71 Å for Ne and Ar, respectively) and to their different ability to enter in “chemical reaction” in the restricted space between the PbI6 octahedra. Acknowledgment. This work was performed in collaboration with Eleonora Polini, Laura Henry, Dmitry Chernyshov, Andrzej Sienkiewicz, Gaetan Giriat, Anastasiia Glushkova. It is supported by the ERC Advanced Grant Picoprop of L.F.

/pdf/high-pressure-transformation-of-mapbi3-role-of-the-noble-gas-2n4sptzm0b.pdf

High-pressure transformation of MAPbI3: role of the noble-gas medium

Einstein's stochastic description of the random movement of small objects in a fluid, i.e. Brownian motion, reveals to be quite different, when observed on short timescales. The limitations of Einstein's theory with respect to particle inertia and hydrodynamic memory yield to the apparition of a colored frequency-dependent component in the spectrum of the thermal forces, which is called "the color of Brownian motion". The knowledge of the characteristic timescales of the motion of a trapped microsphere motion in a Newtonian fluid allowed to develop a high-resolution calibration method for optical interferometry. Well-calibrated correlation quantities, such as the mean square displacement or the velocity autocorrelation function, permit to study the mechanical properties of fluids at high frequencies. These properties are estimated by microrheological calculations based on the theoretical relations between the complex mobility of the beads and the rheological properties of a complex fluid.

http://portal.uned.es/pls/portal/docs/PAGE/UNED_MAIN/LAUNIVERSIDAD/UBICACIONES/01/DOCENTE/PABLO_DOMINGUEZ_GARCIA/TAB22070757/TAB22070761/DOMINGUEZ%20ET%20AL_PROC%20SPIE_2013.PDF

Exploiting the color of Brownian motion for high-frequency microrheology of Newtonian fluids

The alkali fullerides, (AC60)n with A= K, Rb, Cs are conducting crystalline polymers in which covalently bonded ions form parallel linear chains. The polymerization depolymerization transition at about 400 K is reversible. Unlike other alkali fulleride compounds the polymers are stable in air. Structural aspects are discussed together with electron and nuclear magnetic resonance and frequency dependent conductivity. At ambient temperatures all polymers are strongly correlated metals. (KC60)n remains metallic to low temperatures. (RbC60)n and (CsC60)n have a metal insulator transition below 50 K. Magnetic data indicate that these systems may have quasi one dimensional electronic structures and that the ground state is an ordered spin density wave state. The opposing view believes (AC60)n are 3D conductors like doped (CH)x and (SN)x which are anisotropic but are not quasi one dimensional conductors in spite of the linear chain polymeric structure.

Conducting fulleride polymers

We discuss striking, linear resistivity in single crystals of Sr2RuO4−δ that persist over three decades of temperature, up to ∼1050K, while the superconductivity remains confined <1 K This suggests that linear resistivity is not an exclusive feature of the N- state of high-Tc cuprates, but rather of all layered oxides, especially perovskites, possibly even independently of the magnitude of Tc

Anomalous linear resistivity from ∼1 to 103 K in Sr2RuO4−δ

In this chapter we demonstrate the use of optical trapping interferometry to track and study the motion of a Brownian particle down to hydrodynamic timescales, where the response of the surrounding viscous fluid becomes dominant A Brownian particle rapidly explores its surrounding medium that in turn alters its trajectory, and hence functions as a probe of its local environment After an introduction to fundamental aspects of the theory of Brownian motion, which are very often ignored by experimentalists, we describe our instrument with a particular emphasis on position detection, data acquisition and analysis Comparing the suitable theory with our data allows calibration of our instrument and quantification of the influence of experimentally relevant parameters, such as the trapping force constant, the fluid properties and the Brownian particle itself The presented approach should ultimately open up the possibility of using a Brownian probe as a direct reporter of even more complex viscoelastic and/or heterogeneous media


Keywords:

Brownian motion;
optical trapping;
optical tweezers;
colloids;
diffusion;
long time tail;
hydrodynamic memory;
thermal noise probing

László Forró

Papers

High-pressure transformation of MAPbI3: role of the noble-gas medium

Exploiting the color of Brownian motion for high-frequency microrheology of Newtonian fluids

Conducting fulleride polymers

Anomalous linear resistivity from ∼1 to 103 K in Sr2RuO4−δ

Probing Hydrodynamic Fluctuations with a Brownian Particle