The binary progenitor of Tycho Brahe's 1572 supernova

The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion. Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0-G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova.     

Heart rate variability during high-intensity exercise

The aim of this paper is to describe and analyse the behaviour of heart rate variability (HRV) during constant-load, high-intensity exercise using a time frequency analysis (Wavelet Transform). Eleven elite cyclists took part in the study (age: 18.6±3.0 years; VO_2max: 4.88±0.61 litres·min^?1). Initially, all subjects performed an incremental cycloergometer test to determine load power in a constant load-test (379.55±36.02 W; 89.0%). HRV declined dramatically from the start of testing (p <0.05). The behaviour of power spectral density within the LF band mirrored that of total energy, recording a significant decrease from the outset LF peaks fell rapidly thereafter, remaining stable until the end of the test. HF-VHF fell sharply in the first 20 to 30 seconds. The relative weighting (%) of HF-VHF was inverted with the onset of fatigue, [1.6% at the start, 7.1 (p <0.05) at the end of the first phase, and 43.1% (p <0.05) at the end of the test]. HF-VHF_peak displayed three phases: a moderate initial increase, followed by a slight fall, thereafter increasing to the end of the test. The LF/HF-VHF ratio increased at the start, later falling progressively until the end of the first phase and remaining around minimal values until the end of the test.     

表面等离激元共振成像技术在识别和确认诱导多能干细胞生物标记中的应用(英文)

诱导多能干细胞(i PSCs)是再生医学领域,尤其是细胞治疗和药物筛选研究中非常有吸引力的细胞来源.然而,再生医学需要对i PSCs进行快速、精准鉴别.在本研究中,我们开发了针对多能性生物标记物的抗体阵列,分别以胚胎干细胞(ESCs)和鼠成纤维细胞(MEF)裂解液作为阳性和阴性对照,应用快速且无需标记的表面等离激元共振成像(SPRi)技术对i PSCs裂解液中的多种抗原进行检测.每一种抗体都与i PSC裂解液中相应的抗原显示出特异性识别.这一结果表明,SPRi技术适合于检测i PSCs裂解液中的多种抗原,并具有通用性,利用SPRi技术可以用于对干细胞裂解液中生物标志物的高通量鉴别分析.     

Unidirectional molecular motor on a gold surface

Molecules capable of mimicking the function of a wide range of mechanical devices have been fabricated, with motors that can induce mechanical movement attracting particular attention. Such molecular motors convert light or chemical energy into directional rotary or linear motion, and are usually prepared and operated in solution. But if they are to be used as nanomachines that can do useful work, it seems essential to construct systems that can function on a surface, like a recently reported linear artificial muscle. Surface-mounted rotors have been realized and limited directionality in their motion predicted. Here we demonstrate that a light-driven molecular motor capable of repetitive unidirectional rotation can be mounted on the surface of gold nanoparticles. The motor design uses a chiral helical alkene with an upper half that serves as a propeller and is connected through a carbon-carbon double bond (the rotation axis) to a lower half that serves as a stator. The stator carries two thiol-functionalized 'legs', which then bind the entire motor molecule to a gold surface. NMR spectroscopy reveals that two photo-induced cis-trans isomerizations of the central double bond, each followed by a thermal helix inversion to prevent reverse rotation, induce a full and unidirectional 360 degrees rotation of the propeller with respect to the surface-mounted lower half of the system.     

The optical afterglow of the short gamma-ray burst GRB 050709

It has long been known that there are two classes of gamma-ray bursts (GRBs), mainly distinguished by their durations. The breakthrough in our understanding of long-duration GRBs (those lasting more than approximately 2 s), which ultimately linked them with energetic type Ic supernovae, came from the discovery of their long-lived X-ray and optical 'afterglows', when precise and rapid localizations of the sources could finally be obtained. X-ray localizations have recently become available for short (duration <2 s) GRBs, which have evaded optical detection for more than 30 years. Here we report the first discovery of transient optical emission (R-band magnitude approximately 23) associated with a short burst: GRB 050709. The optical afterglow was localized with subarcsecond accuracy, and lies in the outskirts of a blue dwarf galaxy. The optical and X-ray afterglow properties 34 h after the GRB are reminiscent of the afterglows of long GRBs, which are attributable to synchrotron emission from ultrarelativistic ejecta. We did not, however, detect a supernova, as found in most nearby long GRB afterglows, which suggests a different origin for the short GRBs.     

Controlled microfluidic interfaces

The microfabrication technologies of the semiconductor industry have made it possible to integrate increasingly complex electronic and mechanical functions, providing us with ever smaller, cheaper and smarter sensors and devices. These technologies have also spawned microfluidics systems for containing and controlling fluid at the micrometre scale, where the increasing importance of viscosity and surface tension profoundly affects fluid behaviour. It is this confluence of available microscale engineering and scale-dependence of fluid behaviour that has revolutionized our ability to precisely control fluid/fluid interfaces for use in fields ranging from materials processing and analytical chemistry to biology and medicine.     

Infrared phononic nanoantennas: Localized surface phonon polaritons in SiC disks

The electromagnetic interaction of light with polar materials shows a sharp and well defined electromagnetic response in the infrared (IR) region that consists mainly of excitation of optical phonons. Similar to surface plasmons in the visible region, surface phonons can couple efficiently to infrared light in micron-sized antennas made of polar materials. We applied the boundary element method to calculating the infrared electromagnetic response of single SiC disks acting as effective infrared antennas as a function of different parameters such as disk size and thickness. We also analyzed the effect of locating a probing metallic tip near the SiC disk to scatter light in the proximity of the SiC disk, thereby obtaining new spectral peaks connected with localized modes between the tip and the SiC disk. We then further investigated their application in IR scanning probe microscopy. A near-field map of the phononic resonances enhances the understanding of the nature of the IR extinction peaks.     

Genotype, haplotype and copy-number variation in worldwide human populations

Genome-wide patterns of variation across individuals provide a powerful source of data for uncovering the history of migration, range expansion, and adaptation of the human species. However, high-resolution surveys of variation in genotype, haplotype and copy number have generally focused on a small number of population groups. Here we report the analysis of high-quality genotypes at 525,910 single-nucleotide polymorphisms (SNPs) and 396 copy-number-variable loci in a worldwide sample of 29 populations. Analysis of SNP genotypes yields strongly supported fine-scale inferences about population structure. Increasing linkage disequilibrium is observed with increasing geographic distance from Africa, as expected under a serial founder effect for the out-of-Africa spread of human populations. New approaches for haplotype analysis produce inferences about population structure that complement results based on unphased SNPs. Despite a difference from SNPs in the frequency spectrum of the copy-number variants (CNVs) detected--including a comparatively large number of CNVs in previously unexamined populations from Oceania and the Americas--the global distribution of CNVs largely accords with population structure analyses for SNP data sets of similar size. Our results produce new inferences about inter-population variation, support the utility of CNVs in human population-genetic research, and serve as a genomic resource for human-genetic studies in diverse worldwide populations.