122 research outputs found
Mid-infrared optical parametric amplifier using silicon nanophotonic waveguides
All-optical signal processing is envisioned as an approach to dramatically
decrease power consumption and speed up performance of next-generation optical
telecommunications networks. Nonlinear optical effects, such as four-wave
mixing (FWM) and parametric gain, have long been explored to realize
all-optical functions in glass fibers. An alternative approach is to employ
nanoscale engineering of silicon waveguides to enhance the optical
nonlinearities by up to five orders of magnitude, enabling integrated
chip-scale all-optical signal processing. Previously, strong two-photon
absorption (TPA) of the telecom-band pump has been a fundamental and
unavoidable obstacle, limiting parametric gain to values on the order of a few
dB. Here we demonstrate a silicon nanophotonic optical parametric amplifier
exhibiting gain as large as 25.4 dB, by operating the pump in the mid-IR near
one-half the band-gap energy (E~0.55eV, lambda~2200nm), at which parasitic
TPA-related absorption vanishes. This gain is high enough to compensate all
insertion losses, resulting in 13 dB net off-chip amplification. Furthermore,
dispersion engineering dramatically increases the gain bandwidth to more than
220 nm, all realized using an ultra-compact 4 mm silicon chip. Beyond its
significant relevance to all-optical signal processing, the broadband
parametric gain also facilitates the simultaneous generation of multiple
on-chip mid-IR sources through cascaded FWM, covering a 500 nm spectral range.
Together, these results provide a foundation for the construction of
silicon-based room-temperature mid-IR light sources including tunable
chip-scale parametric oscillators, optical frequency combs, and supercontinuum
generators
Unpacking the relationships between impulsivity, neighborhood disadvantage, and adolescent violence : an application of a neighborhood-based group decomposition
The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007–2013)/ERC Grant Agreement no. 615159 (ERC Consolidator Grant DEPRIVEDHOODS, Socio-spatial inequality, deprived neighbourhoods, and neighbourhood effects); and from the Marie Curie programme under the European Union’s Seventh Framework Programme (FP/2007–2013)/Career Integration Grant no. PCIG10-GA-2011-303728 (CIG Grant NBHCHOICE, Neighbourhood choice, neighbourhood sorting, and neighbourhood effects).Scholars have become increasingly interested in how social environments condition the relationships between individual risk-factors and adolescent behavior. An appreciable portion of this literature is concerned with the relationship between impulsivity and delinquency across neighborhood settings. The present article builds upon this growing body of research by considering the more nuanced pathways through which neighborhood disadvantage shapes the development of impulsivity and provides a situational context for impulsive tendencies to manifest in violent and aggressive behaviors. Using a sample of 12,935 adolescent from the National Longitudinal Study of Adolescent to Adult Health (Add Health) (mean age = 15.3, 51% female; 20% Black, 17% Hispanic), we demonstrate the extent to which variation in the association between impulsivity and delinquency across neighborhoods can be attributed to (1) differences in mean-levels of impulsivity and violence and (2) differences in coefficients across neighborhoods. The results of a series of multivariate regression models indicate that impulsivity is positively associated with self-reported violence, and that this relationship is strongest among youth living in disadvantaged neighborhoods. The moderating effect of neighborhood disadvantage can be attributed primarily to the stronger effect of impulsivity on violence in these areas, while differences in average levels of violence and impulsivity account for a smaller, yet nontrivial portion of the observed relationship. These results indicate that the differential effect of impulsivity on violence can be attributed to both developmental processes that lead to the greater concentration of violent and impulsive adolescents in economically deprived neighborhoods as well as the greater likelihood of impulsive adolescents engaging in violence when they reside in economically disadvantaged communities.Publisher PDFPeer reviewe
The skull of Epidolops ameghinoi from the early Eocene Itaboraí fauna, southeastern Brazil, and the affinities of the extinct marsupialiform order Polydolopimorphia
The skull of the polydolopimorphian marsupialiform Epidolops ameghinoi is described
in detail for the first time, based on a single well-preserved cranium and associated left
and right dentaries plus additional craniodental fragments, all from the early Eocene
(53-50 million year old) Itaboraí fauna in southeastern Brazil. Notable craniodental
features of E. ameghinoi include absence of a masseteric process, very small
maxillopalatine fenestrae, a prominent pterygoid fossa enclosed laterally by a
prominent ectopterygoid crest, an absent or tiny transverse canal foramen, a simple,
planar glenoid fossa, and a postglenoid foramen that is immediately posterior to the
postglenoid process. Most strikingly, the floor of the hypotympanic sinus was
apparently unossified, a feature found in several stem marsupials but absent in all
known crown marsupials. "Type II" marsupialiform petrosals previously described from
Itaboraí plausibly belong to E. ameghinoi; in published phylogenetic analyses, these
petrosals fell outside (crown-clade) Marsupialia. "IMG VII" tarsals previously referred to
E. ameghinoi do not share obvious synapomorphies with any crown marsupial clade,
nor do they resemble those of the only other putative polydolopimorphians represented
by tarsal remains, namely the argyrolagids. Most studies have placed
Polydolopimorphia within Marsupialia, related to either Paucituberculata, or to
Microbiotheria and Diprotodontia. However, diprotodonty almost certainly evolved
independently in polydolopimorphians, paucituberculatans and diprotodontians, and
Epidolops does not share obvious synapomorphies with any marsupial order.
Epidolops is dentally specialized, but several morphological features appear to be
more plesiomorphic than any crown marsupial. It seems likely Epidolops that falls
outside Marsupialia, as do morphologically similar forms such as Bonapartherium and
polydolopids. Argyrolagids differ markedly in their known morphology from Epidolops
but share some potential apomorphies with paucituberculatans. It is proposed that
Polydolopimorphia as currently recognised is polyphyletic, and that argyrolagids (and
possibly other taxa currently included in Argyrolagoidea, such as groeberiids and
patagoniids) are members of Paucituberculata. This hypothesis is supported by
Bayesian non-clock phylogenetic analyses of a total evidence matrix comprising DNA
sequence data from five nuclear protein-coding genes, indels, retroposon insertions
and morphological characters: Epidolops falls outside Marsupialia, whereas
argyrolagids form a clade with the paucituberculatans Caenolestes and Palaeothentes,
regardless of whether the Type II petrosals and IMG VII tarsals are used to score
characters for Epidolops or not. There is no clear evidence for the presence of crown
marsupials at Itaboraí, and it is possible that the origin and early evolution of
Marsupialia was restricted to the "Austral Kingdom" (southern South America,
Antarctica, and Australia)
The Development of Criminal Style in Adolescence and Young Adulthood: Separating the Lemmings from the Loners
Despite broad consensus that most juvenile crimes are committed with peers, many questions regarding developmental and individual differences in criminal style (i.e., co-offending vs. solo offending) remain unanswered. Using prospective 3-year longitudinal data from 937 14- to 17-year-old serious male offenders, the present study investigates whether youths tend to offend alone, in groups, or a combination of the two; whether these patterns change with age; and whether youths who engage in a particular style share distinguishing characteristics. Trajectory analyses examining criminal styles over age revealed that, while most youth evinced both types of offending, two distinct groups emerged: an increasingly solo offender trajectory (83%); and a mixed style offender trajectory (17%). Alternate analyses revealed (5.5%) exclusively solo offenders (i.e., only committed solo offenses over 3 years). There were no significant differences between groups in individuals’ reported number of friends, quality of friendships, or extraversion. However, the increasingly solo and exclusively solo offenders reported more psychosocial maturity, lower rates of anxiety, fewer psychopathic traits, less gang involvement and less self reported offending than mixed style offenders. Findings suggest that increasingly and exclusively solo offenders are not loners, as they are sometimes portrayed, and that exclusively solo offending during adolescence, while rare and previously misunderstood, may not be a risk factor in and of itself
The Short-Term Dynamics of Peers and Delinquent Behavior: An Analysis of Bi-weekly Changes Within a High School Student Network
Comparison of Brazilian and American norms for the International Affective Picture System (IAPS)
Unpacking the Relationships between Impulsivity, Neighborhood Disadvantage, and Adolescent Violence: An Application of a Neighborhood-Based Group Decomposition
Risk factors associated with early mortality in patients with multiple myeloma who were treated upfront with a novel agents containing regimen
Outcomes following small bowel obstruction due to malignancy in the national audit of small bowel obstruction
Introduction
Patients with cancer who develop small bowel obstruction are at high risk of malnutrition and morbidity following compromise of gastrointestinal tract continuity. This study aimed to characterise current management and outcomes following malignant small bowel obstruction.
Methods
A prospective, multicentre cohort study of patients with small bowel obstruction who presented to UK hospitals between 16th January and 13th March 2017. Patients who presented with small bowel obstruction due to primary tumours of the intestine (excluding left-sided colonic tumours) or disseminated intra-abdominal malignancy were included. Outcomes included 30-day mortality and in-hospital complications. Cox-proportional hazards models were used to generate adjusted effects estimates, which are presented as hazard ratios (HR) alongside the corresponding 95% confidence interval (95% CI). The threshold for statistical significance was set at the level of P ≤ 0.05 a-priori.
Results
205 patients with malignant small bowel obstruction presented to emergency surgery services during the study period. Of these patients, 50 had obstruction due to right sided colon cancer, 143 due to disseminated intraabdominal malignancy, 10 had primary tumours of the small bowel and 2 patients had gastrointestinal stromal tumours. In total 100 out of 205 patients underwent a surgical intervention for obstruction. 30-day in-hospital mortality rate was 11.3% for those with primary tumours and 19.6% for those with disseminated malignancy. Severe risk of malnutrition was an independent predictor for poor mortality in this cohort (adjusted HR 16.18, 95% CI 1.86 to 140.84, p = 0.012). Patients with right-sided colon cancer had high rates of morbidity.
Conclusions
Mortality rates were high in patients with disseminated malignancy and in those with right sided colon cancer. Further research should identify optimal management strategy to reduce morbidity for these patient groups
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