Search

Numerous studies of rotating detonation engines (RDEs) have noted the appearance of weaker secondary waves which travel with or counter to the primary wave system. These secondary waves can affect the speed, strength, multiplicity, and directional preference of the primary wave system, all of which have implications for engine performance and operability. As such, understanding the formation and stabilization of different wave modes is critical for developing practical RDE systems. To this end, the present work uses an adaptive mesh refinement framework to simulate two-dimensional unwrapped RDEs at high spatial resolution. Four injection configurations are considered, including a simplified continuous injection boundary, as well as three discrete injection setups with varying injector diameter and spacing. In the discrete injection cases, the effects of mass flow rate and near-wave grid resolution are also investigated. Continuous injection is found to produce a single wave, while discrete injection yields increasing numbers of co- and counter-propagating waves when the number of injectors or the reactant flow rate increases. The generation of secondary waves is linked to acoustic reflections associated with wave passage over the discrete injectors, as well as successive “micro-explosions” that occur when a reaction zone recouples to a shock wave traversing a reactant jet. These secondary waves can then coalesce in the presence of fresh reactants, providing a mechanism for new primary waves to form and the directional preference of the wave system to switch. The diameter and spacing of the injectors directly impact the sustained propagation of the primary waves, as well as the availability of reactants needed to form a strong counter-propagating wave system. The unsteadiness induced by the different injection schemes is manifested in conditional statistics for heat release and heat release rate, which show enhanced deflagrative combustion in discrete injection configurations.

The interplay between mass injection, heat release, and boundary layer development plays a key role in dictating the dynamics and stability of confined supersonic flows. The relative impacts of these factors and the timescales over which they influence the upstream and downstream flow can provide critical insights into how different operating modes develop. As such, this work presents a series of simulations of an experimental axisymmetric direct connect flowpath. The mass flow rates and chemical compositions of the injection stages are varied, and subsequent information propagation and mode transitions are analyzed using spatiotemporal correlations of cross-sectional-averaged quantities. Increasing the injection flow rate decreases the time lags and durations of positive correlations between pressure and heat release at various points along the flowpath. Meanwhile, in dual-mode cases with lower injection flow rates, these correlations develop after longer time delays and persist for a longer times, illustrating how information propagates more gradually in these scenarios. Over the full flowpath, positive correlations persist for comparatively long times between (1) the upstream isolator pressure and the pressure elsewhere, and (2) the pressure in the downstream diverging combustor section and the upstream pressure. As such, the influence of the pressure in the intermediate constant-area combustor section decays more rapidly. Conditional statistics suggest that flow blockage and pressurization from the injected mass reduce the local ignition delay, thereby facilitating increased pressurization via heat release in a positive feedback loop.

Procedural memory, which is rooted in the basal ganglia, underlies the learning and processing of numerous automatized motor and cognitive skills, including in language. Not surprisingly, disorders with basal ganglia abnormalities have been found to show impairments of procedural memory. However, brain abnormalities could also lead to atypically enhanced function. Tourette syndrome (TS) is a candidate for enhanced procedural memory, given previous findings of enhanced TS processing of grammar, which likely depends on procedural memory. We comprehensively examined procedural learning, from memory formation to retention, in children with TS and typically developing (TD) children, who performed an implicit sequence learning task over two days. The children with TS showed sequence learning advantages on both days, despite a regression of sequence knowledge overnight to the level of the TD children. This is the first demonstration of procedural learning advantages in any disorder. The findings may further our understanding of procedural memory and its enhancement. The evidence presented here, together with previous findings suggesting enhanced grammar processing in TS, underscore the dependence of language on a system that also subserves visuomotor sequencing.

The advent of data-based modeling has provided new methods and algorithms for analyzing the complex flow fields in high-speed combustion applications. These techniques can be used to study the fluid dynamics and reaction progress in different regions of the flow, which can provide insight into the underlying physics of the system while helping one identify avenues for the development and application of new models. The present work implements two such algorithms – the standard K-means clustering algorithm and a modified Jacobian-scaled K-means clustering algorithm – to analyze a high-speed reacting flow field. The results show that the Jacobian-scaled K-means algorithm allocates more clusters in the regions of the thermochemical state space where chemical source term is highest. In physical space, this concentrates the flow partitions in regions where heat release rate is higher and chemical timescales are lower. This is observed for different cluster numbers and data sets. When moving between data sets that occupy different portions of the state space, the cluster centroid locations are found to be less sensitive to the data set when the Jacobian-scaled K-means algorithm is used. Altogether, the modified K-means algorithm provides a new tool for identifying thermodynamic and thermochemical similarities in and across compressible reactive flow fields.

Meta-analysis and meta-regression were used to evaluate whether evidence to date demonstrates deficits in procedural memory in individuals with specific language impairment (SLI), and to examine reasons for inconsistencies of findings across studies. The Procedural Deficit Hypothesis (PDH) proposes that SLI is largely explained by abnormal functioning of the frontal-basal ganglia circuits that support procedural memory. It has also been suggested that declarative memory can compensate for at least some of the problems observed in individuals with SLI. A number of studies have used Serial Reaction Time (SRT) tasks to investigate procedural learning in SLI. In this report, results from eight studies that collectively examined 186 participants with SLI and 203 typically-developing peers were submitted to a meta-analysis. The average mean effect size was .328 (CI95: .071, .584) and was significant. This suggests SLI is associated with impairments of procedural learning as measured by the SRT task. Differences among individual study effect sizes, examined with meta-regression, indicated that smaller effect sizes were found in studies with older participants, and in studies that had a larger number of trials on the SRT task. The contributions of age and SRT task characteristics to learning are discussed with respect to impaired and compensatory neural mechanisms in SLI.

According to the Procedural Deficit Hypothesis (PDH), abnormalities of brain structures underlying procedural memory largely explain the language deficits in children with specific language impairment (SLI). These abnormalities are posited to result in core deficits of procedural memory, which in turn explain the grammar problems in the disorder. The abnormalities are also likely to lead to problems with other, non-procedural functions, such as working memory, that rely at least partly on the affected brain structures. In contrast, declarative memory is expected to remain largely intact, and should play an important compensatory role for grammar. These claims were tested by examining measures of working, declarative and procedural memory in 51 children with SLI and 51 matched typically-developing (TD) children (mean age 10). Working memory was assessed with the Working Memory Test Battery for Children, declarative memory with the Children’s Memory Scale, and procedural memory with a visuo-spatial Serial Reaction Time task. As compared to the TD children, the children with SLI were impaired at procedural memory, even when holding working memory constant. In contrast, they were spared at declarative memory for visual information, and at declarative memory in the verbal domain after controlling for working memory and language. Visuo-spatial short-term memory was intact, whereas verbal working memory was impaired, even when language deficits were held constant. Correlation analyses showed neither visuo-spatial nor verbal working memory was associated with either lexical or grammatical abilities in either the SLI or TD children. Declarative memory correlated with lexical abilities in both groups of children. Finally, grammatical abilities were associated with procedural memory in the TD children, but with declarative memory in the children with SLI. These findings replicate and extend previous studies of working, declarative and procedural memory in SLI. Overall, we suggest that the evidence largely supports the predictions of the PDH.

The cortex constituting Broca's area does not exist in isolation. Rather, like other cortical regions, Broca's area is connected to other brain structures, which likely play closely related functional roles. This paper focuses on the basal ganglia, a set of subcortical structures that project through topographically organized “channels” via the thalamus to different frontal regions. It is hypothesized that the basal ganglia project to Broca's area. This circuitry is further posited to encompass at least two channels. One channel can be characterized as subserving procedural memory, while the other underlies the retrieval of knowledge from declarative memory. These hypotheses are supported by both anatomical and functional evidence. Implications and issues for further investigation are discussed.

Specific Language Impairment (SLI) has been explained by two broad classes of hypotheses, which posit either a deficit specific to grammar, or a non-linguistic processing impairment. Here we advance an alternative perspective. According to the Procedural Deficit Hypothesis (PDH), SLI can be largely explained by the abnormal development of brain structures that constitute the procedural memory system. This system, which is composed of a network of interconnected structures rooted in frontal/basal-ganglia circuits, subserves the learning and execution of motor and cognitive skills. Crucially, recent evidence also implicates this system in important aspects of grammar. The PDH posits that a significant proportion of individuals with SLI suffer from abnormalities of this brain network, leading to impairments of the linguistic and non-linguistic functions that depend on it. In contrast, functions such as lexical and declarative memory, which depend on other brain structures, are expected to remain largely spared. Evidence from an in-depth retrospective examination of the literature is presented. It is argued that the data support the predictions of the PDH, and particularly implicate Broca's area within frontal cortex, and the caudate nucleus within the basal ganglia. Finally, broader implications are discussed, and predictions for future research are presented. It is argued that the PDH forms the basis of a novel and potentially productive perspective on SLI.

Nouns may refer to countable objects such as tables, or to mass entities such as rice. The mass/count distinction has been discussed in terms of both semantic and syntactic features encoded in the mental lexicon. Here we show that event-related potentials (ERPs) can reflect the processing of such lexical features, even in the absence of any feature-related violations. We demonstrate that count (vsmass) nouns elicit a frontal negativity which is independent of the N400 marker for conceptual-semantic processing, but resembles anterior negativities related to grammatical processing. This finding suggests that the brain differentiates between count and mass nouns primarily on a syntactic basis.

In the most extensive investigation to date of language in global amnesia, we acquired data from experimental measures and examined longitudinal data from standardized tests, to determine whether language function was preserved in the amnesic patient H.M. The experimental measures indicated that H.M. performed normally on tests of lexical memory and grammatical function, relative to age‐ and education‐matched control participants. Longitudinal data from four Wechsler subtests (Information, Comprehension, Similarities, and Vocabulary), that H.M. had taken 20 times between 1953 (preoperatively) and 2000, indicated consistent performance across time, and provided no evidence of a lexical memory decrement. We conclude that medial temporal lobe structures are not critical for retention and use of already acquired lexical information or for grammatical processing. They are, however, required for acquisition of lexical information, as evidenced in previous studies revealing H.M.'s profound impairment at learning new words. Hippocampus 2001;11:347–360. © 2001 Wiley‐Liss, Inc.

This article presents findings from analyses of nationwide data on employment discrimination charges filed under the Americans With Disabilities Act (ADA). In conducting the analyses, emphasis was placed on understanding the extent to which the ADA charge process differentially affects individuals with psychiatric disabilities. We found that 16.3% of individuals whose charges were closed as of June 30, 1995, received benefits from filing charges; individuals with psychiatric disabilities were only somewhat less likely to experience benefits from filing charges than were individuals with nonpsychiatric disabilities; individuals with schizophrenia had a strikingly lower benefit rate than all other individuals with other types of psychiatric disorders; and there was considerable variation among individuals with different kinds of nonpsychiatric disabilities in benefit rates.

Motor nerve conduction velocity (MCV) and nerve fibre calibre spectra of peripheral nerves were determined at different ages, during development in normal and protein-deprived rats. The protein deprivation was achieved by feeding female rats a protein deficient diet, given ad lib from 2 weeks before conception and onwards. After weaning, the offspring were fed the same protein-deficient diet. Compared to control rats which were given a balanced diet, the protein-deprived rats showed considerably reduced body weights but moderately reduced values of albumin and total protein in serum at 6 and 15 weeks of age. Although essentially the same, the mean nerve fibre diameter of the studied dorsal tail nerve was slightly larger in the protein-deprived rats at 6 weeks of age than in controls, while the inverse relationship was found at 15 weeks of age. The increase of MCV in normal and protein-deprived rats followed essentially the same curve during the period from 5–30 weeks of age. The results indicate that the MCV and nerve fibre diameter during development are correlated to chronological age and not to body size, although protein deprivation may, to a minor extent, influence nerve fibre calibre growth.

We report a case of restoration of vision in an amblyopic eye after cataract extraction and intraocular lens insertion after a traumatic event resulting in no light perception vision in the contralateral eye. The timing and indication for cataract removal in amblyopic eyes has not been well established. Because this patient was a special case, surgery was the only measure that could be taken to improve the patient's sight. Safe cataract surgery is never without risk and was approached with a long discussion and educational opportunity with the patient. Fortunately, the patient's vision and quality of life greatly improved. To our knowledge, this is the first report of a case in which such a unique decision was encountered.