Magnetic-field enhancement of performance of superconducting nanowire single-photon detector

We present SNSPDs from NbN nanowires shaped after square-spiral that allows an increase not only in critical currents but also an extension of spectral detection efficiencies by just applying an external magnetic field. Using negative electron-beam lithography with the positive resist for shaping nanowires, made it possible to reduce the inner bend radius. Consequently, the effect of critical-current enhancement in the magnetic field becomes stronger than it was demonstrated earlier. Here we achieved a 13% increase of the critical current in the magnetic field. We measured spectra of the single-photon detection efficiency in the wavelength range from 400 to 1100 nm in the magnetic field. At zero field, the square spiral has the spectrum similar to that of a meander. At the field providing the maximum of the critical current, the detection efficiency and the cut-off wavelength in the spectrum increase by 20% and by 54%, correspondingly. The magnetic-field dependence of dark count rate is well described by proposed analytical model

Geometrical jitter and bolometric regime in photon detection by straight superconducting nanowire

We present a direct observation of the geometrical jitter in single photon detection by a straight superconducting nanowire. Differential measurement technique was applied to the 180-{\mu}m long nanowire similar to those commonly used in the technology of superconducting nanowire single photon detectors (SNSPD). A non-gaussian geometrical jitter appears as a wide almost uniform probability distribution (histogram) of the delay time (latency) of the nanowire response to detected photon. White electrical noise of the readout electronics causes broadened, Gaussian shaped edges of the histogram. Subtracting noise contribution, we found for the geometrical jitter a standard deviation of 8.5 ps and the full width at half maximum (FWHM) of the distribution of 29 ps. FWHM corresponds to the propagation speed of the electrical signal along the nanowire of $6.2\times10^{6}$ m/s or 0.02 of the speed of light. Alternatively the propagation speed was estimated from the central frequency of the measured first order self-resonance of the nanowire. Both values agree well with each other and with previously reported values. As the intensity of the incident photon flux increases, the wide probability distribution collapses into a much narrower Gaussian distribution with a standard deviation dominated by the noise of electronics. We associate the collapse of the histogram with the transition from the discrete, single photon detection to the uniform bolometric regim

Magnetic-field enhancement of performance of superconducting nanowire single-photon detector

We present SNSPDs from NbN nanowires shaped after square-spiral that allows an increase not only in critical currents but also an extension of spectral detection efficiencies by just applying an external magnetic field. Using negative electron-beam lithography with the positive resist for shaping nanowires, made it possible to reduce the inner bend radius. Consequently, the effect of critical-current enhancement in the magnetic field becomes stronger than it was demonstrated earlier. Here we achieved a 13% increase of the critical current in the magnetic field. We measured spectra of the single-photon detection efficiency in the wavelength range from 400 to 1100 nm in the magnetic field. At zero field, the square spiral has the spectrum similar to that of a meander. At the field providing the maximum of the critical current, the detection efficiency and the cut-off wavelength in the spectrum increase by 20% and by 54%, correspondingly. The magnetic-field dependence of dark count rate is well described by proposed analytical model

Adapting wheat in Europe for climate change

Increasing cereal yield is needed to meet the projected increased demand for world food supply of about 70% by 2050. Sirius, a process-based model for wheat, was used to estimate yield potential for wheat ideotypes optimized for future climatic projections (HadCM3 global climate model) for ten wheat growing areas of Europe. It was predicted that the detrimental effect of drought stress on yield would be decreased due to enhanced tailoring of phenology to future weather patterns, and due to genetic improvements in the response of photosynthesis and green leaf duration to water shortage. Yield advances could be made through extending maturation and thereby improve resource capture and partitioning. However the model predicted an increase in frequency of heat stress at meiosis and anthesis. Controlled environment experiments quantify the effects of heat and drought at booting and flowering on grain numbers and potential grain size. A current adaptation of wheat to areas of Europe with hotter and drier summers is a quicker maturation which helps to escape from excessive stress, but results in lower yields. To increase yield potential and to respond to climate change, increased tolerance to heat and drought stress should remain priorities for the genetic improvement of wheat

Abnormal Response of Costal Chondrocytes to Acidosis in Patients with Chest Wall Deformity

Costal cartilage is much understudied compared to the load bearing cartilages. Abnormally grown costal cartilages are associated with the inherited chest wall deformities pectus excavatum and pectus carinatum resulting in sunken or pigeon chest respectively. A lack of understanding of the ultrastructural and molecular biology properties of costal cartilage is a major confounder in predicting causes and outcomes of these disorders. Due to the avascular nature of cartilage, chondrocytes metabolize glycolytically, producing an acidic environment. During physical activity hydrogen ions move within cartilage driven by compressive forces, thus at any one time, chondrocytes experience transient changes in pH. A variety of ion channels on chondrocytes plasma membrane equip them to function in the rapidly changing conditions they experience. In this paper we describe reduced expression of the ASIC2 gene encoding the acid sensing ion channel isoform 2 (previously referred to as ACCN1 or ACCN) in patients with chest wall deformities. We hypothesized that chondrocytes from these patients cannot respond normally to changes in pH that are an integral part of the biology of this tissue. Activation of ASICs indirectly creates a cascade ultimately dependent on intracellular calcium transients. The objective of this paper was to compare internal calcium signaling in response to external pH changes in costal chondrocytes from patients with chest wall deformities and healthy individuals. Although the molecular mechanism through which chondrocytes are regulated by acidosis remains unknown, we observed reduced amplitudes of calcium rise in patient chondrocytes exposed to low pH that become further impaired upon repeat exposure

Effect of Dehydrated Trehalose Matrix on the Kinetics of Forward Electron Transfer Reactions in Photosystem I

The effect of dehydration on the kinetics of forward electron transfer (ET) has been studied in cyanobacterial photosystem I (PS I) complexes in a trehalose glassy matrix by time-resolved optical and EPR spectroscopies in the 100 fs to 1 ms time domain. The kinetics of the flash-induced absorption changes in the subnanosecond time domain due to primary and secondary charge separation steps were monitored by pump–probe laser spectroscopy with 20-fs low-energy pump pulses centered at 720 nm. The back-reaction kinetics of P700 were measured by high-field time-resolved EPR spectroscopy and the forward kinetics of A∙−1A/A∙−1B→FX by time-resolved optical spectroscopy at 480 nm. The kinetics of the primary ET reactions to form the primary P∙+700A∙−0 and the secondary P∙+700A∙−1 ion radical pairs were not affected by dehydration in the trehalose matrix, while the yield of the P∙+700A∙−1 was decreased by ~20%. Forward ET from the phylloquinone molecules in the A∙−1A and A∙−1B sites to the iron–sulfur cluster FX slowed from ~220 ns and ~20 ns in solution to ~13 μs and ~80 ns, respectively. However, as shown by EPR spectroscopy, the ~15 μs kinetic phase also contains a small contribution from the recombination between A∙−1B and P∙+700. These data reveal that the initial ET reactions from P700 to secondary phylloquinone acceptors in the A- and B-branches of cofactors (A1A and A1B) remain unaffected whereas ET beyond A1A and A1B is slowed or prevented by constrained protein dynamics due to the dry trehalose glass matrix

Temporally and genetically discrete periods of wheat sensitivity to high temperature

Successive single day transfers of pot-grown wheat to high temperature (35/30oC day/night) replicated controlled environments, from the second node detectable to the milky-ripe growth stages, provides the strongest available evidence that the fertility of wheat can be highly vulnerable to heat stress during two discrete peak periods of susceptibility: early booting (decimal growth stage (GS) 41-45) and early anthesis (GS 61-65). A double Gaussian fitted simultaneously to grain number and weight data from two contrasting elite lines (Renesansa, listed in Serbia, Ppd-D1a, Rht8; Savannah, listed in UK, Ppd-D1b, Rht-D1b) identified peak periods of main stem susceptibility centred on 3 (s.e.= 0.82) and 18 (s.e. = 0.55) days (mean daily temperature = 14.3oC) pre-GS 65 for both cultivars. Severity of effect depended on genotype, growth stage and their interaction: grain set relative to that achieved at 20/15oC dropped below 80% for Savannah at booting and Renesansa at anthesis. Savannah was relatively tolerant to heat stress at anthesis. A further experiment including 62 lines of the mapping, doubled-haploid progeny of Renesansa x Savannah found tolerance at anthesis to be associated with Ppd-D1b, Rht-D1b, and a QTL from Renesansa on chromosome 2A. None of the relevant markers were associated with tolerance during booting. Rht8 was never associated with heat stress tolerance, a lack of effect confirmed in a further experiment where Rht8 was included in a comparison of near isogenic lines in a cv. Paragon background. Some compensatory increases in mean grain weight were observed, but only when stress was applied during booting and only where Ppd-D1a was absent

Local Atomic Mechanism for the Diffusion Jump of Carbon Atom in Austenite

A carbon atom diffusion jump in iron austenite was considered as a subsequence of transformations between the cementite structure and the regular FCC packing. A model of this transformation was based on a 2D model of the elemental act of a polymorph transformation in metals. The energy threshold of this transformation has been calculated using the Morse pair potential. It occurs that the estimated enthalpy of the transformation is equal to 149±20 kJ/mole which is in satisfactory agreement with experimental data