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 email@example.com
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.
We report four cases of Taenia saginata taeniasis in different urban communities of Aragua state, Venezuela. After subsequent treatment with praziquantel and a saline purge, adult tapeworms were collected from all four patients and demonstrated to be T. saginata by morphological and molecular characterization. The finding of T. saginata in four distinct and separate urban municipalities of the Aragua state indicates the pertinence of rigorous meat inspection, and the importance of establishing parasite prevalence in human and bovine Venezuelan populations.
This paper investigates the impact of the wall-heating conditions on the heat transfer performance of a rotating channel with one side smooth and one side roughened by 45° inclined ribs. Previous experimental and numerical studies for single-ribbed wall-heated channels showed that rotation has a significant negative impact on heat transfer performance. In order to investigate this uncommon behaviour, RANS simulations were conducted under three different wall-heating conditions in the present study: ribbed wall heated, all walls heated and adiabatic conditions. Numerical results show that the presence of uneven wall-heating conditions has a negligible impact on the stationary case, but it has a large influence on rotational cases, in both, the heat transfer and the flow field. The underlying reason is that in rotating cases, uneven heating results in different buoyancy effects on the trailing and leading walls of the channel that alter the main flow velocity profile. As a consequence, also secondary flows and heat transfer performance are affected.
The unsteady laminar flow between two large rotating disks when one of them is impulsively started is described using the von Kármán similarity analysis to reduce the solution of the Navier–Stokes equations to a set of ordinary differential equations. It is found that the transient phenomenon consists of three distinct phases. Firstly, the development of the Ekman boundary layer, where a quasi-steady Stewartson-type of flow is created. Secondly, angular momentum is initially diffused in the axial direction until the inward radial convection of angular momentum becomes dominating. Thirdly, a Batchelor flow is created once the Bödewadt boundary layer is developed and the entrainment of disk and stator boundary layers are balanced. The dependences of the characteristic dimensionless times on the Reynolds number based on the cavity gap for the second and third stages have been identified numerically and analytically. It is found that the diffusive part of the transient is bypassed if the flow, initially at rest, is perturbed with a small circumferential velocity. The flow and heat transfer transient during a ramp of finite duration has been computed numerically. The integral angular momentum and energy balances of the cavity have been performed in order to understand the energy and momentum budget of the cavity. It is concluded that the spin-up and the spin-down process of a rotor–stator cavity using a quasi-stationary approximation of the fluid, where the time derivatives are neglected, is questionable for realistic gas turbine applications. Finally, the self-similar solution is compared against two-dimensional axisymmetric, steady and unsteady, laminar simulations to assess the limitations and validity of the self-similar analysis. It has been identified that in a closed squared cavity the outer shroud modifies the physics of the transient, but the general conclusions drawn from the one-dimensional model are still valid.
Strongyloides venezuelensis is a parasitic nematode of rodents that is frequently used to obtain heterologous antigens for immunological diagnosis of human strongyloidiasis. The aim of this study was to identify antigens from filariform larvae of S. venezuelensis for immunodiagnosis of human strongyloidiasis. Soluble and membrane fractions from filariform larvae of S. venezuelensis were obtained in phosphate saline (SS and SM) and in Tris–HCl buffer (TS and TM), and were analysed by Western blotting. Different antigenic components were recognized by IgG antibodies from the sera of strongyloidiasis patients. Highest recognition was observed for a 30–40 kDa mass range present in all antigenic fractions. The band encompassing this mass range was then excised and subjected to mass spectrometry for protein identification. Immunoreactive proteins identified in the soluble fractions corresponded to metabolic enzymes, whereas cytoskeletal proteins and galectins were more abundant in the membrane fractions. These results represent the first approach towards identification of S. venezuelensis antigens for use in immunodiagnostic assays for human strongyloidiasis.
As a first step to study the influence that rotation has in the evolution of the most massive stars, we obtained the projected rotational velocity (v sin i) of a sample of OB stars from clusters and associations. We found that most of our stars present v sin i lower than 200 km/s.
Early life stress (ELS) is consistently associated with increased risk for subsequent psychopathology. Individual differences in neural response to reward may confer vulnerability to stress-related psychopathology. Using data from the ongoing Duke Neurogenetics Study, the present study examined whether reward-related ventral striatum (VS) reactivity moderates the relationship between retrospectively reported ELS and anhedonic symptomatology. We further assessed whether individual differences in reward-related VS reactivity were associated with other depressive symptoms and problematic alcohol use via stress-related anhedonic symptoms and substance use-associated coping.
Blood oxygen level-dependent functional magnetic resonance imaging (fMRI) was collected while participants (n = 906) completed a card-guessing task, which robustly elicits VS reactivity. ELS, anhedonic symptoms, other depressive symptoms, coping behavior, and alcohol use behavior were assessed with self-report questionnaires. Linear regressions were run to examine whether VS reactivity moderated the relationship between ELS and anhedonic symptoms. Structural equation models examined whether this moderation was indirectly associated with other depression symptoms and problematic alcohol use through its association with anhedonia.
Analyses of data from 820 participants passing quality control procedures revealed that the VS × ELS interaction was associated with anhedonic symptoms (p = 0.011). Moreover, structural equation models indirectly linked this interaction to non-anhedonic depression symptoms and problematic alcohol use through anhedonic symptoms and substance-related coping.
These findings suggest that reduced VS reactivity to reward is associated with increased risk for anhedonia in individuals exposed to ELS. Such stress-related anhedonia is further associated with other depressive symptoms and problematic alcohol use through substance-related coping.
We present experimental and theoretical Raman spectra of natural graphite mineral of Sonora, Mexico. In this work, we take the advantage of the utility of the RAMAN spectroscopy as a technique to determine the crystallinity and structure of graphite mineral. The RAMAN spectroscopy provides information that can be used to determine the degree of graphitization, which in turn can be used to know the metamorphic degree of the host rock. The resulting RAMAN spectra of graphite were divided in first and second order regions, in the first region (1100-1800cm-1) the E2g vibration mode with D6h crystal symmetry occurs at 1580cm-1 (G band) that indicates poorly organized graphite, additional bands appears in the first order region at 1350 cm-1 (D band) called the defect band, and another at 1620 cm-1 (D* band). The second-order region (2200-3400cm-1) shows several bands at ~2400 ~2700 ~2900 ~3300cm-1, all of them attributed to electron-phonon interactions or combination scattering. The density functional theory calculations were applied to determine the vibrational properties and the stacking layers of graphite.
We present a joint experimental and theoretical study dedicated to analyze the properties of Boron-Nitride (BN) nanotubes. First, multi-walled boron-nitride (MWBN) nanotubes were prepared by means of a modified electric arc discharge technique using boron-nitride powder. In a first stage, the BN powder was subjected to a ball milling process for about 100 hours in an atmosphere of ammonia. Later on, BN nanoparticle formation took place after the preparation of a pressed pellet at 300 °C to 25 kPa which was sintered in a furnace at approximately 1000 °C in nitrogen atmosphere for 15 hrs. The pellets were subsequently incorporated to the electrical arc discharge set up to obtain the MWBN nanotubes. The as-prepared MWBN nanotubes samples were characterized by scanning electron microscope, X-ray photoelectron spectroscopy, and micro RAMAN spectroscopy. Second, and in order to understand the measured data, extensive density functional theory calculations were performed. We present low energy atomic configurations for model finite-length armchair, zigzag, and chiral single-walled BN nanotubes, as well as for two-dimensional BN sheets. We calculate the vibrational spectra and the optical gap of each one of our considered structures and reveal how precise details of the local atomic environment can be revealed. Finally, we consider BN nanotubes functionalized with NH2, glycine and S-H molecules. We present the structural characteristics of the adsorbed configurations, charge transfer effects, and the electronic behavior. We conclude by underlining the crucial role played by molecular functionalization in order to tune the properties of these kinds of systems.
Hybrid piezoelectric composites were obtained by embedding barium titanate (BTO) nanofibers into a polyvinylidene fluoride (PVDF) matrix. Green BTO fibers were obtained by electrospinning a precursor polymeric solution under an electric field of 1 kV/cm. A network of non-woven ceramic BTO fibers was obtained after calcination of the green fibers. A PVDF solution was deposited over the ceramic fibers by spin-coating and then subjected to a low temperature heat treatment, to evaporate the solvent and promote the crystallization of the polar beta phase of PVDF.
In average, the diameter of the ceramic fibers ranged from 105 to 225 nm, presenting ribbon-like shape in some cases. Crystalline phases of BTO and PVDF were confirmed by X-ray diffraction and infrared spectroscopy, respectively. Polarization hysteresis curves revealed a ferroelectric behavior in all samples.
Low-energy displacement cascades in zircon (ZrSiO4) initiated by a Zr primary knock-on atom have been investigated by molecular dynamics (MD) simulations using a Coulombic model for long-range interactions, Buckingham potential for short-range interactions and Ziegler-Biersack potentials for close pair interactions. Displacements are found to occur mainly in the O sublattice, and O replacements by a ring mechanism are predominant. Clusters containing Si interstitials bridged by O interstitials, vacancy clusters and anti-site defects are found to occur. This Si-O-Si bridging is considerable in ZrSiO4 quenched from the melt in MD simulations.
A study of vacancy defect formation is carried out using a density functional theory molecular dynamics simulation methodology. The objective is to study the effects of electronic excitations in crystalline and non-crystalline silica polymorphs. We present an initial study focusing on the formation energetics of distinct oxygen vacancy defect states in α-quartz.
A study of vacancy defect migration pathways and energetics in a-quartz is carried out using an empirical simulation methodology that is coupled with the nudged elastic band method. Results from this study indicate that the migration pathway for migration is between adjacent sites. We anticipate the results will guide modifications to empirical potentials for use in the study of point defect formation of more complex systems.
Linear rheological behavior and Microrheology measurements of sodium salt calf-thymus DNA aqueous solutions as a function of concentration are reported here. The microrheological behavior was obtained by a combination of experimental techniques: mechanical Rheometry and Dynamic light scattering (DLS). The viscoelastic properties of DNA in water as a function of concentration were performed at 20 °C and rheological and microrhelogical curves were performed. The result indicated that for concentrations lower than the entanglement concentration (Ce) the system exhibits a predominantly viscous behavior, whereas for higher concentrations exhibits a predominantly elastic behavior. The plateau modulus (G0) and the zero complex viscosity () follow a power law concentration dependence of the form: and , respectively The microrheology results overlap perfectly in a single line with the mechanical rheology results, extending the time resolution to faster breathing modes
VIHI: the Visible and Infrared Hyperspectral Imager is one of the three channels of the Simbio-Sys instrument for the BepiColombo mission to Mercury. Its scientific objective is to study the hermean surfaces composition by sensing the photon flux reflected off the planet. VIHI works in the range of 400 to 2000 nm with a spectral resolution around a few hundreds.
The particularity of this channel is the use of a single detector matrix (264 × 264) for both visible and infrared wavelengths. Getting the visible part of the detector responsivity is achieved by thinning an infrared HgCdTe matrix because visible light is completely absorbed inside the substrate. The thinning process is well controlled since a long time and was used to increase number of thermal cycle of the hybrid devices. Recently, this process is able to remove completely the substrate and, thus, open the detector to the visible range. The detector is a custom design made by Raytheon Vision System in Goleta (USA). In this paper, we will describe the expected performances of the detector which is designed to work in the very harsh radiation environment of Mercury.
We consider an M/G/1 retrial queue with
finite capacity of the retrial group. We derive the Laplace transform of
the busy period using the catastrophe method. This is the key point for
the numerical inversion of the density function and the computation of
moments. Our results can be used to approach the corresponding descriptors
of the M/G/1 queue with infinite retrial group,
for which direct analysis seems intractable.
The occurrence of amber in Sierra de Cantabria (álava, Basque Country) has been known for more than two decades but biological inclusions have only recently been found. The existence of crustaceans (amphipods and isopods), chelicerates (acari and arachnids), 12 orders of insects, and several bird feathers are reported in this preliminary study. In addition, there are leaf remains, molluscs, and a fair number of inorganic inclusions.
Pollen analysis of the clastic series indicates an age between upper Aptian—middle Albian, which allows an assignment of this stratigraphic unit to the Nograro Formation. Chemical analysis indicates that the amber has high maturity, which reflects its Cretaceous age. Chemical composition analysis also indicates an araucariacean origin, which is corroborated by pollen found within the amber deposit.
This new fossil site provides information for the reconstruction of paleocommunities of arthropods and sedimentary environments in the extreme south of the Basque-Cantabrian Basin during the Lower Cretaceous, characterized by coniferous forests with an understory of vascular cryptograms. Some of the identified arthropods add to the fossil record for various groups that are poorly known or unknown for this time period. This Lagerstätte constitutes one of the most important deposits of Mesozoic amber in the world.
There is a growing interest in queueing systems with negative arrivals; i.e. where the arrival of a negative customer has the effect of deleting some customer in the queue. Recently, Harrison and Pitel (1996) investigated the queue length distribution of a single server queue of type M/G/1 with negative arrivals. In this paper we extend the analysis to the context of queueing systems with request repeated. We show that the limiting distribution of the system state can still be reduced to a Fredholm integral equation. We solve such an equation numerically by introducing an auxiliary ‘truncated’ system which can easily be evaluated with the help of a regenerative approach.
Single server queues with repeated attempts are useful in
the modeling of computer and telecommunication systems. In addition, we
consider in this paper the possibility of disasters. When a disaster
occurs, all the customers present in the system are destroyed
immediately. Using a regenerative approach, we derive a numerically
stable recursion scheme for the state probabilities. This model can be
employed to analyze the behaviour of a buffer in computers with virus
Queueing systems with repeated requests have many useful applications in communications and computer systems modeling. In the majority of previous work the repeat requests are made individually by each unsatisfied customer. However, there is in the literature another type of queueing situation, in which the time between two successive repeated attempts is independent of the number of customers applying for service. This paper deals with the M/G/1 queue with repeated orders in its most general setting, allowing the simultaneous presence of both types of repeat requests. We first study the steady state distribution and the partial generating functions. When the service time distribution is exponential we show that the performance characteristics can be expressed in terms of hypergeometric functions.