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.
Porphyrinic compounds are of increasing interest to the materials science community, yet little attention has been paid to crystallographically controlled voids and channels in these materials. We have conducted an initial survey of the voids and channels in a random subset of 1000 porphyrinic compounds with known crystal structures. From calculations using a rolling-probe subroutine, we have found that about 5% of these compounds have line-of-sight channels, which differ in their topology depending on the crystallography. A small but significant number of porphyrinic compounds have calculated void contents of >25 volume %. We discuss in detail the void and channel characteristics, including pore-size distribution, of four representative compounds, with technological implications.
The Yale–Potsdam Stellar Isochrones (YaPSI) cover the low and intermediate stellar mass regime (0.15 to 5.0 M⊙) for a wide range of solar-scaled chemical compositions (metallicity from −0.5 to +0.3; helium mass fraction from 0.25 to 0.37, assigned independently of each other). The tracks are finely spaced in mass, to allow for accurate interpolation. The models feature state-of-the-art input physics relevant to low-mass stars modeling (surface boundary conditions, equation of state), thus updating the faint end of the Yonsei-Yale (YY) isochrones. Utility codes, such as an isochrone interpolator in age, metallicity and helium content, are also provided. The YaPSI isochrones are in good agreement with the empirical mass–luminosity and mass–radius relations available to date, and provide satisfactory fitting of the color-magnitude diagrams of well-studied open clusters.
Cognitive deficits are a core feature of schizophrenia, and impairments in most domains are thought to be stable over the course of the illness. However, cross-sectional evidence indicates that some areas of cognition, such as visuospatial associative memory, may be preserved in the early stages of psychosis, but become impaired in later established illness stages. This longitudinal study investigated change in visuospatial and verbal associative memory following psychosis onset.
In total 95 first-episode psychosis (FEP) patients and 63 healthy controls (HC) were assessed on neuropsychological tests at baseline, with 38 FEP and 22 HCs returning for follow-up assessment at 5–11 years. Visuospatial associative memory was assessed using the Cambridge Neuropsychological Test Automated Battery Visuospatial Paired-Associate Learning task, and verbal associative memory was assessed using Verbal Paired Associates subtest of the Wechsler Memory Scale - Revised.
Visuospatial and verbal associative memory at baseline did not differ significantly between FEP patients and HCs. However, over follow-up, visuospatial associative memory deteriorated significantly for the FEP group, relative to healthy individuals. Conversely, verbal associative memory improved to a similar degree observed in HCs. In the FEP cohort, visuospatial (but not verbal) associative memory ability at baseline was associated with functional outcome at follow-up.
Areas of cognition that develop prior to psychosis onset, such as visuospatial and verbal associative memory, may be preserved early in the illness. Later deterioration in visuospatial memory ability may relate to progressive structural and functional brain abnormalities that occurs following psychosis onset.
We have used a four-band photometric system capable of distinguishing C, S, and M stars to undertake a survey of AGB stars in M31. We discuss the results from this survey and from follow-up spectroscopy.
Carbon nanotube (CNT)-reinforced aluminum composite powders were synthesized by cryogenic milling. The effects of different milling parameters and CNT contents on the structural characteristics and mechanical properties of the resulting composite powders were studied. Detailed information on powder morphology and the dispersion and structural integrity of the CNTs is crucial for many powder consolidation methods, particularly cold spray, which is increasingly utilized to fabricate metal-based nanocomposites. While all of the produced composite powders exhibited particle sizes suitable for spray applications, it was found that with increasing CNT content, the average particle size decreased and the size distribution became narrower. The dispersion of CNTs improved with milling time and helped to maintain a small Al grain size during cryogenic milling. Although extensive milling allowed for substantial grain size reduction, the process caused notable CNT degradation, leading to a deterioration of the mechanical properties of the resulting composite.
Whether there are differential effects of first-generation antipsychotics (FGAs) and second-generation antipsychotics (SGAs) on the brain is currently debated. Although some studies report that FGAs reduce grey matter more than SGAs, others do not, and research to date is limited by a focus on schizophrenia spectrum disorders. To address this limitation, this study investigated the effects of medication in patients being treated for first-episode schizophrenia or affective psychoses.
Cortical thickness was compared between 52 first-episode psychosis patients separated into diagnostic (i.e. schizophrenia or affective psychosis) and medication (i.e. FGA and SGA) subgroups. Patients in each group were also compared to age- and sex-matched healthy controls (n = 28). A whole-brain cortical thickness interaction analysis of medication and diagnosis was then performed. Correlations between cortical thickness with antipsychotic dose and psychotic symptoms were examined.
The effects of medication and diagnosis did not interact, suggesting independent effects. Compared with controls, diagnostic differences were found in frontal, parietal and temporal regions. Decreased thickness in FGA-treated versus SGA-treated groups was found in a large frontoparietal region (p < 0.001, corrected). Comparisons with healthy controls revealed decreased cortical thickness in the FGA group whereas the SGA group showed increases in addition to decreases. In FGA-treated patients cortical thinning was associated with higher negative symptoms whereas increased cortical thickness in the SGA-treated group was associated with lower positive symptoms.
Our results suggest that FGA and SGA treatments have divergent effects on cortical thickness during the first episode of psychosis that are independent from changes due to illness.
Engaging patients in first-episode psychosis services is critical in maximising the effect of early intervention and establishing a framework for longer-term treatment. Biopsychosocial assessments determine a working diagnosis and inform evidence-based treatment. Atypical antipsychotics should be used at doses that maximise therapeutic benefit and adherence while minimising side-effects. Patients are helped to construct a narrative of their illness, including a shared understanding of the contribution of biological and environmental risks, and early warning signs. Common comorbid conditions, including depression, suicidal ideation, substance misuse and anxiety, should be addressed. Management of comorbid borderline and antisocial personality disorders is difficult; their nexus with psychosis is discussed. Cognitive–behavioural therapy is a mainstay of treatment, with specific interventions developed for problems typical in first-episode presentations. Core psychosocial interventions include psychoeducation, vocational and educational support, family interventions and multimodal group programmes.
Early intervention services were established on the basis of a number of fundamental principles, including the notions that intervening in the early stages of psychosis alters illness trajectory and prognosis, that multicomponent interventions promote psychosocial recovery and reduce iatrogenic damage, and that early targeting of non-responders reduces treatment resistance. There is growing evidence of the benefits of specialised early intervention services. These include improved clinical, social and vocational outcomes, reduced in-patient stays and better engagement. Early intervention services can also significantly reduce the risk of a second episode and are highly valued by service users and carers. Duration of treatment appears to determine long-term outcome and there remains uncertainty about how long such intensive intervention should last and whether all patients need the same length of care. Budgetary constraints are pervasive and are particularly likely to affect prodrome clinics and community awareness programmes.
The atomic arrangement and electronic structure in the vicinity of Ni(111)- ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) interfaces have been studied by atomistic simulation and by first-principles Density Functional theory. “Depth Profiling” is carred out in both methodologies, to determine modifications of cohesive energy and electron distribution of atomic layers from the interface plane. The energy profiling results show the interface consists of only a few atomic layers. Simulation results and electron density analyses are in good agreement with High Resolution Spatially Resolved Electron Microscopy data.
Laser-assisted deposition of GaAs, AlAs and [AIGa]As thin films on Ge(100) substrates from trimethylgallium-trimethylarsenic and trimethylaluminumtrimethylarsenic Lewis acid-base adduct source materials is reported. A parametric study has been performed in which reactive gas pressure, substrate temperature, laser fluence, laser wavelength (248 nm or 193 nm). and orientation of the laser beam with respect to the substrate have been varied. In the case of irradiation parallel to the substrate, stoichiometric films of GaAs and [AIGa]As have been obtained. The data suggest that for irradiation perpendicular to the substrate a competition exists between desorption and photodeposition, which adversely affects film stoichiometry under the conditions studied.
The fracture results of an amorphous epoxy resin and polycrystalline silicon nitride tested under monotonically increasing crack mouth opening displacements were compared. A conventional compact tension specimen was used for the epoxy. A new loading system and specimen was designed for the ceramic to permit stable crack growth. Tests conducted on both materials revealed multiple events of subcritical crack growth, dynamic initiation, dynamic growth, and subsequent arrest. The elastic energy release rate at initiation, G11, and arrest, G1a, was evaluated for each event. The value of G11 was found to be higher than G1a for both materials.
Also common was the systematic existence of slow growth prior to dynamic initiation. Additionally, both materials showed differences between the fracture surface morphology for slow, 10-6 m/s, and fast, 103 m/s, growth. Although a constant G1a was recorded for the epoxy, large scatter and a possible trend was recorded for G1a in the ceramic.
It is shown that the composition and structure of CdTe and CdS surfaces can be reversibly controlled by excimer laser irradiation at fluences below the melting threshold. The removal rate is observed to depend exponentially on laser fluence up to the melting threshold. The translational energies of products desorbed from laser-irradiated CdTe surfaces were determined using time-of-flight spectrometry and are well-described by a Maxwellian velocity distribution. The dynamics of the photo-stimulated desorption process are correlated with the laser-induced changes in composition, and it is shown that the data are consistent with a thermal mechanism for desorption. A model is introduced which describes the reversible, fluence-dependent changes in composition and structure in terms of the kinetic competition between formation and desorption processes at the semiconductor surface.
Gas-phase UV-initiated (193 nm) photodissociations of methyl (CH3) and trifluoromethyl (CF3) containing compounds have been investigated for the dry etching of single crystal GaAs substrates. Etching rates of greater than 1 μ/min. have been observed. Etching rates and surface profiles will be discussed in terms of crystal orientation, reactive etching fragments, and laser-surface interactions. Products of the etching reactions have been examined by UV absorption, mass spectrometry and laser-induced fluorescence techniques. Applications to large scale and micron dimension etching processes will be briefly discussed.
Reinforcing phases used to strengthen a metal matrix cannot be appreciably chemically reactive for the times and temperatures expected during the service life of the composite. Where accurate phase diagrams exist that describe the interactions of the metal matrix and the reinforcing phase, the evaluation process can be completed with these diagrams and, if reactivity is encountered, with appropriate kinetic parameters. These complete phase diagrams are rarely available for complex materials systems. Therefore, we have adopted several ways of using available thermochemical data to estimate the compatibility of various metal matrix composite systems. Usually evaluations involve comparing matrix component activities, using reinforcing phase component thermochemistry to decide whether or not a reaction is expected by examining product chemical activities. Other methods use integral thermochemical properties of reactants and possible products in estimations. In either case a single thermodynamically favored reaction will disqualify a reinforcing phase on an energetic basis if not a kinetic basis. Where no disqualifying reactions are found, the reinforcing phase-metal matrix system is considered a candidate to be proved or disproved in experimental studies which may reveal reaction products not included in the extensive but still limited thermochemical literature. This approach has been advantageously applied to several systems. The study of Ti-Al metal matrices with selected reinforcing phases is discussed as an example.
We have investigated the dynamics of KrF excimer laser ablation of CdTe and the fluence dependent changes in surface stoichiometry that accompany the laser ablation process. The composition of the CdTe surface was reversibly controlled between stoichiometric and a Te-rich condition by varying the laser fluence over the range from 15–65 mJ/cm2. The primary species ejected from the irradiated surface were Cd atoms and Te2 molecules. Their velocity distributions as measured by time-of-flight mass spectrometry were found to be Maxwellian. From the analysis of the velocity distributions, the preferential desorption of surface atoms, and the reversible nature of the process, we conclude that the desorption is due to a photo-thermal mechanism which mediates the competition between Te2 formation and desorption and the desorption of Cd atoms.
In this paper we discuss the use of optical-based flux monitoring (OFM) for real-time control of atomic antimony fluxes for applications in molecular beam epitaxy. Atomic antimony beams were generated using a two-zone cracking effusion cell. The product distribution of the source was characterized using a time-of-flight mass spectrometer employing resonance-enhanced laser ionization. A double-pass OFM system has been developed to monitor the atomic antimony beam that is capable of precise flux measurement during MBE growth.
We investigated the induced magnetic behaviour of the Ag of Fe/Ag multilayers with low temperature nuclear orientation. The experiments show induced magnetic moments in all samples. Furthermore, multilayers with 2ML and 4ML of Ag, these moments do not lie in the plane of the multilayer at low external magnetic fields.
Nb-silicide based composites have excellent potential for future high-temperature structural applications. Nb-silicide composites possess Nb together with high-strength silicides, such as Nb5Si3 and Nb3Si. Alloying elements such as Ti and Hf, are added to obtain a balance of properties such as creep performance and oxidation resistance. In Nb-silicide composites generated from Nb-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. The present paper describes a low temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3 possesses the hP16 structure, as opposed to the tI32 structure observed in binary Nb5Si3.