Book chapters will be unavailable on Saturday 24th August between 8am-12pm BST. This is for essential maintenance which will provide improved performance going forwards. Please accept our apologies for any inconvenience caused.
To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Blowing snow was produced artificially in a cold wind-tunnel, and various measurements were conducted including particle diameters, concentrations, saltation lengths heat transport and electric charge. The mean diameter of blowing snow particles decreased only slightly with increasing height; in the saltation layer, standard deviation was large and velocities were scattered in a wide range, suggesting the complex dynamic process on taking-off. The mean saltation length ranged from a few cm to 40 cm increasing with wind velocity.
When wind blew without snow drifting, the static air pressure on the snow surface was smaller at higher levels, the vertical pressure gradient being negative. The pressure gradient became positive when blowing snow was initiated eg +9.6 Pa/m at 11.2 m/s and -8.3 °C. The magnitude of à downward force acting on a saltating snow partice caused by the pressure gradient was not large enough to explain the downward acceleration found from photographic analyses of particle trajectories.
Blowing snow particles were charged negatively the magnitude of charge increased with lowering temperature. Increase in vertical heat transfer was found in blowing snow by measuring the temperature of the air at various levels; the increase is reflected on that in the apparent turbulent diffusion coefficient.
Gamma Cassiopeiae is an enigmatic Be star with unusually hard, strong X-ray emission compared with normal main-sequence B stars. The origin has been debated for decades between two theories: mass accretion onto a hidden compact companion and a magnetic dynamo driven by the star-Be disk differential rotation. There has been no decisive signature found that supports either theory, such as a pulse in X-ray emission or the presence of large-scale magnetic field. In a ~100 ksec duration observation of the star with the Suzaku X-ray observatory in 2011, we detected six rapid X-ray spectral hardening events called “softness dips”. All the softness dip events show symmetric softness ratio variations, and some of them have flat bottoms apparently due to saturation. The softness dip spectra are best described by either ~40% or ~70% partial covering absorption to kT ~12 keV plasma emission by matter with a neutral hydrogen column density of ~2 − 8 × 1021cm−2, while the spectrum outside of these dips is almost free of absorption. This result suggests that two distinct X-ray emitting spots in the γ Cas system, perhaps on a white dwarf companion with dipole mass accretion, are occulted by blobs in the Be stellar wind, the Be disk, or rotating around the white dwarf companion. The formation of a Be star and white dwarf binary system requires mass transfer between two stars; γ Cas may have experienced such activity in the past.
The existence of multiple subclasses of type Ia supernovae (SNeIa) has been the subject of great debate in the last decade. In this work, we show how machine learning tools facilitate identification of subtypes of SNe Ia. Using Deep Learning for dimensionality reduction, we were capable of performing such identification in a parameter space of significantly lower dimension than its principal component analysis counterpart. This is evidence that the progenitor system and the explosion mechanism can be described with a small number of initial physical parameters. All tools used here are publicly available in the Python package DRACULA (Dimensionality Reduction And Clustering for Unsupervised Learning in Astronomy) and can be found within COINtoolbox (https://github.com/COINtoolbox/DRACULA).
Since the discovery of fading X-rays from Gamma-Ray Bursts (GRBs) with BeppoSAX (Piro et al. 1997, Costa et al. 1997), world-wide follow-up observations in optical band have achieved the fruitful results. The case of GRB 970228, there was an optical transient, coincides with the BeppoSAX position and faded (Paradijs et al. 1997, Sahu et al. 1997). These optical observations also confirmed the extended component, which was associated with the optical transient. The new transient are fading with a power-law function in time and the later observation of HST confirmed the extended emission is stable (Fruchter et al. 1997). This extended object seems to be a distant galaxy and strongly suggests to be the host.
In the previous work, it is reported that the Spin-Seebeck effect (SSE), which refer to the generation of a spin current from a temperature gradient, can be enhanced by Fe interface treatment. Here, we investigated the Fe thickness (dFe) dependency of spin-Seebeck voltage (VSSE) and mixing conductance (gr) in Pt/Fe/Bi:YIG/SGGG system. As a result, magnitude of VSSE had a peak at dFe ≓ 1 ML (monolayer , ≓ 0.3 mm), and also increase of gr was saturated at this point. It suggests that VSSE increase with increasing gr when dFe is smaller than 1.0 ML. For the case in which dFe is larger than 1.0ML, however, VSSE decreases due to a spin current decay in Fe layer with a constant gr. These experimental results are consistent with previous theoretical works.
The second order theory of coupling is discussed regarding the radial pulsation of stellar models which are constructed ignoring convection. The formula including the nonadiabatic effect is presented. Numerical values given for model classical cepheids are considerably greater than the adiabatic values.
A large outbreak of enterohaemorrhagic Escherichia coli (EHEC) O111 and O157 occurred in Japan in April 2011. We conducted an unmatched case-control study and trace-back investigation to determine the source of EHEC O111 infection and risk factors for severe complications. Pulsed-field gel electrophoresis was performed to help define cases. A total of 86 individuals met the case definition. Of these, 40% experienced haemolytic uraemic syndrome (HUS), 24% acute encephalopathy, and 6% died. Illness was significantly associated with eating the raw beef dish yukhoe (odds ratio 19·64, 95% confidence interval 7·03–54·83), the likely food vehicle. EHEC O111 and its closely related stx-negative variants were found in the beef. HUS occurred most frequently in individuals aged 5–9 years, and this age group was significantly associated with acute encephalopathy. The prevalence of HUS and acute encephalopathy was higher than in previous non-O157-related outbreaks, indicating a high risk of severe complications.
To describe a case of giant cell reparative granuloma of the temporal bone which extended into the middle-ear cavity, and which was successfully treated surgically via a transmastoid approach, with hearing preservation.
A 37-year-old man presented with a one-year history of right-sided hearing loss, complicated by a three-month history of otalgia and a sensation of aural fullness. Computed tomography and magnetic resonance imaging demonstrated an osteolytic tumour lesion in the right temporal bone. The diagnosis was confirmed by biopsy from the mastoid lesion.
Investigation and intervention:
Pure-tone audiometry, computed tomography and magnetic resonance imaging were conducted, followed by total resection.
The giant cell reparative granuloma of the temporal bone was completely resected, with preservation of hearing.
Although this patient's giant cell reparative granuloma of the temporal bone extended into the middle-ear cavity, total resection was achieved, with preservation of hearing. To the best of our knowledge, hearing preservation following resection of giant cell reparative granuloma of the temporal bone has not previously been reported.
We report the formation and optical properties of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition for application to single photon sources. InAs/GaAs QD-in-NWs with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μeV are observed. Light emission from the single QD-in-NW shows photon antibunching which evidences single photon emission from high-quality QD-in-NWs.
In this paper we review studies aiming at elucidation of the mechanisms responsible for anomalously low pressure coefficients of the light emission energy, dEE/dP, observed in quantum structures of InGaN/GaN and GaN/AlGaN. We have established that in hexagonal InGaN/GaN and GaN/AlGaN structures the main mechanism involved is related to the pressure induced increase of the piezoelectric field which determines also the strong red shift of the emission energy with thickness of the quantum well. To reproduce the experimental findings in InGaN/GaN case, it is necessary to take into account the dependence of the piezoelectric constants on the volume-conserving strain. Whereas the experimental results on a decrease of dEE/dP in GaN/AlGaNstructures can be fully accounted for within the linear elasticity theory. In contrast to these findings, dEE/dP magnitude measured in cubic InGaN/GaN quantum structures shows value close to changes of the InGaN bangap with pressure obtained from first principle calculations. The latter result is consistent with the absence of the built-in electric fields in the cubic nitride structures.
Optical properties of fully-strained wurtzite and zincblende InxGa1-xN/GaN multiple quantum well (MQW) structures were compared to discuss the origin of exciton localization. In contrast to the hexagonal InGaN MQWs, the photoluminescence (PL) peak energy of cubic InGaN MQWs showed a moderate blueshift with decreasing well thickness, L, and low-temperature PL decay time of the cubic MQWs did not depend strongly on L. The results imply that the wavefunction overlap in cubic InGaN MQWs was not reduced compared to the hexagonal ones, since they do not suffer from the electric field normal to the QW plane due either to spontaneous or piezoelectric polarization. Both MQWs exhibited a large and composition-dependent bandgap bowing, and time-resolved PL (TR-PL) signals showed a stretched-exponential decay even at room temperature. The exciton localization is considered to be an intrinsic property of InGaN.
The arsenic dose dependence of electrical properties for implanted samples at 500°C and subsequently annealed at 1600°C for 30min has been investigated to derivate the activation energies of the arsenic donors in silicon carbide. Hall effect measurements were performed between 20K and 773K. Hall carrier concentration of implanted sample with high dose of 7×1015 cm−2 is independence of temperature, which indicates the formation of implanted layer with metallic conduction. For the sample with low dose of 1×1014 cm−2, the experimental Hall mobility varies directly as T3/2 below 80K and as T−3/2 above 150K. The activation energies of arsenic donors determined from the implanted sample with low dose using a least-squares fit of the charge neutrality equation are 66.8 meV for hexagonal site and 127.0 meV for cubic site, respectively.
Heteroepitaxial A1203 thin films were grown successfully on Si(lO0) substrates by low—pressure chemical vapor deposition (LP—CVD). The growth was performed at a pressure of 30 Torr by pyrolysis of N2 bubbled AI(CH3)3 and N20 at substrate temperatures above 1000ºC.RHEED patterns indicated that the grown films were ɤ—Al203 single crystals with an orientation relationship of ɤ—Al203(l00)//Si(l00). The ɤ—A1203 films were stable and did not show phase transition after a 1140ºC heat—treatment for 2hr. MOS capacitors with 500—Å—thick A1203 films as a gate insulator showed highfrequency capacitance—voltage (C—V) curves without hysteresis. The A1203 interface state density determined from quasi—static C—V measurements was 1.7 X 1011cm-2eV-1. It can be seen that ɤ—Al203 film is a promising new insulator for Si on Insulator (SOI) structures.
Detailed DLTS measurements have revealed the presence of threedifferent midgap levels, labeled EOI, EO2 and EO3, in LEC n-GaAs. The variations of EOl and EO2 concentrations, which are EL2 and ELO in Lagowski's terminology, do not correlate with the distributions of the optical absorption coefficient across wafers, while that of EO3 exhibits good correlation. This suggests that EO3 is the optically detected midgap level. Furthermore, preliminary charged particle activation analysis of oxygen content in GaAs shows that the presence of EO2 (ELO) is not attributed to oxygen. Concentrations of these levels all increase with arsenic mole fraction in the melt.
Residual stress in molecular beam epitaxially (MBE) grown GaAs films on 4°-off (100)Si substrates is investigated with X-ray diffraction technique. It is experimentally confirmed that the GaAs lattice suffers tetragonal deformation with the c-axis being . The GaAs lattice tilts by approximately 0.2° towards the tilted direction of the substrate. It is found that two-dimensional compressive stress dominates in GaAs films thinner than 0.3 μm in thickness, while two-dimensional tensile stress dominates in thicker films. The variation of the stress is understood in terms of a combination of misfit stress and thermal stress. The residual tensile stress is larger than 1 × 109 dyn/cm2 in the films thicker than I pm. The effect of the stress on the reliability of semiconductor laser diodes is discussed.
Deposition of SiNx films by ArF laser induced chemical vapor deposition has been investigated. The films exhibit excellent electrical properties; the high breakdown voltage and the low fixed charge are the same as in films deposited by LPCVD, but the BHF etching rate of them is larger by a factor about 4 than that prepared by the plasma CVD. The diffusion length of the radicals contributing to the deposition was estimated from the distribution of the deposition rate as a function of the deposition parameters. The optical emission from the radicals produced by ArF laser irradiation was also studied. Using these results, we discuss the mechanism of the deposition.
The enhanced disordering of GaAs/AlGaAs superlattices by diffusion of Zn or Si has been reported by many authors. In the case of Si diffusion, the Si can be introduced during epitaxial growth, by implantation, or by diffusion from a sputtered Si mask. In this paper ion implantation is investigated, and the effect of rapid thermal annealing (RTA), used to minimize Si diffusion while eliminating the implant damage, is compared with furnace annealing (FA). Using low temperature photoluminescence (PL) and SIMS, it is found that no disordering of a GaAs/Al0.5Ga0.5As superlattice takes place for a 2 sec anneal at 900°C, and very minimal partial disordering is observed (reproducibly) for a 10 sec anneal at 970°C. This is in sharp contrast with the FA case (850°C for 30 min), for which significant disordering occurs. The PL spectra show luminescence from both GaAs and GaAs/Al0.5Ga0.5As layers in the case of high-temperature RTA suggesting that recrystallization has occurred without disorder, whereas strong emission is observed after FA which corresponds to a disordered layer of average-composition GaAs/Al0.15Ga0.25As In both cases, PL indicates that annealing of the implant damage has occurred. Thus, damage can be eliminated either with or without disordering the superlattice by using FA or RTA, respectively. This is important for 2-D electron gas structures, for which no broadening of the hetero-interface is desired.