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We report the first experiments on divergent shock-driven Richtmyer–Meshkov instability (RMI) at well-controlled single-mode interfaces. These experiments are performed in a novel divergent shock tube designed by shock dynamics theory. Generally, the perturbation growth can be divided into three successive stages: linear growth, quick reduction in growth rate and instability freeze-out. It is observed that the growth rate at each stage is far lower than its counterpart in planar or convergent geometry due to geometric divergence. We also found that nonlinearity is much weaker than that in planar or convergent RMI, and has a negligible influence on the overall amplitude growth even at late stages when it has become strong. This weak nonlinear effect is because the growth of the third harmonic counteracts its feedback to the fundamental mode. As a consequence, the linear theory of Bell (report no. LA-1321) accounting for geometric divergence and Rayleigh–Taylor (RT) stabilization caused by flow deceleration can reasonably predict the present results from early to late stages. The instability freeze-out at late times is ascribed to the negative growth induced by geometric divergence and RT stabilization, and is also well reproduced by the linear theory.
The variable stiffness actuator (VSA) is helpful to realize the post-collision safety strategies for safe human–robot interaction.1 The stiffness of the robot will be reduced to protect the user from injury when the collision between the robot and human occurs. However, The VSA has a mechanism limit constraint that can cause harm to users even if the stiffness is minimized. Accordingly, in this article, a concept combining danger index and robust fault detection and isolation is presented and applied to active–passive variable stiffness elastic actuator (APVSEA). APVSEA can actively change joint stiffness with the change of danger index. Experimental results show that this concept can effectively confirm the fault mode and provide additional protection measures to ensure the safety of users when the joint stiffness has been adjusted to the minimum.
Schizotypy refers to schizophrenia-like traits below the clinical threshold in the general population. The pathological development of schizophrenia has been postulated to evolve from the initial coexistence of ‘brain disconnection’ and ‘brain connectivity compensation’ to ‘brain connectivity decompensation’.
In this study, we examined the brain connectivity changes associated with schizotypy by combining brain white matter structural connectivity, static and dynamic functional connectivity analysis of diffusion tensor imaging data and resting-state functional magnetic resonance imaging data. A total of 87 participants with a high level of schizotypal traits and 122 control participants completed the experiment. Group differences in whole-brain white matter structural connectivity probability, static mean functional connectivity strength, dynamic functional connectivity variability and stability among 264 brain sub-regions of interests were investigated.
We found that individuals with high schizotypy exhibited increased structural connectivity probability within the task control network and within the default mode network; increased variability and decreased stability of functional connectivity within the default mode network and between the auditory network and the subcortical network; and decreased static mean functional connectivity strength mainly associated with the sensorimotor network, the default mode network and the task control network.
These findings highlight the specific changes in brain connectivity associated with schizotypy and indicate that both decompensatory and compensatory changes in structural connectivity within the default mode network and the task control network in the context of whole-brain functional disconnection may be an important neurobiological correlate in individuals with high schizotypy.
A vocabulary acquisition learning activity was designed and a learning system featuring image-to-text recognition technology to support the activity was developed. The effectiveness of the system with regard to facilitating vocabulary acquisition was tested. The perceptions of learners toward this tool and the affordances of the system for vocabulary acquisition were also explored. To this end, we designed an experiment in which 40 native speakers of Russian learning English as a foreign language from an elementary school participated. They were assigned to either a control condition or an experimental condition. All learners learned new vocabulary in class and then applied their new knowledge to contexts with a realistic simulation of the real world by completing a learning task. The learners in the control group used a traditional approach (e.g. the learners learned vocabulary from corresponding pictures in a textbook), whereas the learners in the experimental group used the proposed learning system (e.g. the learners learned vocabulary using the system). A pre-test–post-test/delayed post-test design was employed to test the effectiveness of the treatment on vocabulary acquisition. Learner perceptions and perceived affordances of the system for vocabulary acquisition were explored through a questionnaire survey and interviews. The quantitative results showed that the learners in the experimental group outperformed their counterparts on both the vocabulary post-test and delayed post-test. The qualitative results revealed that most learners in the experimental group had positive perceptions of the system. In addition, the qualitative results showed the three main categories of affordances. Based on these results, several suggestions and implications are provided for the teaching and research community.
Maternal supraphysiological estradiol (E2) environment during pregnancy leads to adverse perinatal outcomes. However, the influence of oocyte exposure to high E2 levels on perinatal outcomes remains unknown. Thus, a retrospective cohort study was conducted to explore the effect of high E2 level induced by controlled ovarian stimulation (COH) on further outcomes after frozen embryo transfer (FET). The study included all FET cycles (n = 10,581) between 2014 and 2017. All cycles were categorized into three groups according to the E2 level on the day of the human Chorionic Gonadotropin trigger. Odds ratios (ORs) and their confidence intervals (CIs) were calculated to evaluate the association between E2 level during COH and pregnancy outcomes and subsequent neonatal outcomes. From our findings, higher E2 level was associated with lower percentage of chemical pregnancy, clinical pregnancy, ongoing pregnancy, and live birth as well as increased frequency of early miscarriage. Preterm births were more common among singletons in women with higher E2 level during COH (aOR1 = 1.93, 95% CI: 1.22–3.06; aOR2 = 2.05, 95% CI: 1.33–3.06). Incidence of small for gestational age (SGA) was more common in both singletons (aOR1 = 2.01, 95% CI: 1.30–3.11; aOR2 = 2.51, 95% CI: 1.69–3.74) and multiples (aOR1 = 1.58, 95% CI: 1.03–2.45; aOR2 = 1.99, 95% CI: 1.05–3.84) among women with relatively higher E2 level. No association was found between high E2 level during COH and the percentage of macrosomia or large for gestational age. In summary, oocyte exposure to high E2 level during COH should be brought to our attention, since the pregnancy rate decreasing and the risk of preterm birth and SGA increasing following FET.
Associations have been shown between father’s absence and menarcheal age, but most studies have focused on absence resulting from divorce, abandonment or death. Little research has been conducted to evaluate the effect on menarcheal age of paternal absence through migrant work. In a sample of 400 middle school students, this study examined the association between paternal migrant work and menarcheal age against a backdrop of extensive rural-to-urban migration in China. Data were collected through a self-reported questionnaire, including social-demographic characteristics, aspects of family relationships, information about father’s migrant work and age at menarche. After adjusting for BMI, parent marital status and perceived relationship with mother, lower self-perceived quality of father–daughter relationship (both ‘father present, relationship poor’ and ‘father absent, relationship poor’) and lower frequency of contact with the father were associated with higher odds for early menarche. These findings suggest that the assumption that father’s absence for work influences the timing of menarche needs to be examined in the context of the quality of the father–daughter relationship and paternal care, which appear to play a critical role in the timing of menarche. These findings also emphasize the importance of enhancing paternal involvement and improving father–daughter relationships in the development of appropriate reproductive strategy in daughters.
Attention-deficit hyperactivity disorder (ADHD) increases the risk of suicidal behaviours through psychiatric comorbidities; however, a significant direct association has not been observed between ADHD and suicide attempts.
To evaluate the risk of suicide attempt in adolescents and young adults with ADHD.
Using a nationwide, population-based insurance claims database, this longitudinal cohort study enrolled 20 574 adolescents and young adults with ADHD and 61 722 age- and gender-matched controls between 2001 and 2009. Any suicide attempt was identified from enrolment to 31 December 2011. The association between ADHD medications and the likelihood of suicide attempt was assessed.
ADHD was an independent risk factor for any suicide attempt (hazard ratio = 3.84, 95% CI = 3.19–4.62) and repeated suicide attempts (hazard ratio = 6.52, 95% CI = 4.46–9.53). Subgroup analyses of men, women, adolescents and young adults demonstrated the same trend. Methylphenidate or atomoxetine treatment did not increase the risk of suicide attempt or repeated suicide attempts. Long-term methylphenidate treatment was associated with a significantly decreased risk of repeated suicide attempts in men (hazard ratio = 0.46, 95% CI = 0.22–0.97).
ADHD was a risk factor for suicide attempt and a stronger predictor of repeated suicide attempts, independent of comorbidities. Further investigation is warranted to explore the mechanism underlying the association between ADHD and suicidal behaviours.
Apathy is a condition characterized by a lack of motivation that manifests in emotional, behavioral, and cognitive domains. Although previous studies have indicated that apathy is associated with frontal lesions, few studies have focused on the different subdomains of apathy, and no in vivo human biochemical data have been obtained to examine the neurochemical changes related to apathy in patients with Alzheimer's disease (AD). Thus, we investigated the frontal neurochemical alterations related to apathy among patients with AD using proton magnetic resonance spectroscopy (1H MRS).
Apathy was assessed through the Apathy Evaluation Scale (AES). 1H MRS was performed to measure neurochemical metabolite levels in the anterior cingulate region and right orbitofrontal region. Associations between neurochemical metabolites and the total score and subscores of each domain of the AES were analyzed.
Altogether, 36 patients completed the study. Patients with lower N-acetylaspartate/creatine ratios (NAA/Cr) in the anterior cingulate region demonstrated higher total apathy scores (β = −0.56, p = 0.003) with adjustments for age, gender, educational level, dementia severity, and depression severity. In a further analysis, a lower NAA/Cr in the anterior cingulate region was associated with all subdomains of apathy, including cognition (β = −0.43, p = 0.028), behavior (β = −0.55, p = 0.002), and emotion (β = −0.50, p = 0.005). No statistically significant associations were discovered in the right orbitofrontal region.
Our results suggest that apathy, in each of its cognitive, behavioral, or emotional subdomains is associated with brain neurochemical alterations in the anterior cingulate region. Abnormal neuronal integrity over the anterior cingulate cortex may exhibit a central role in causing all aspects of apathy in patients with AD.
A stalagmite with high 238U content from Yangkou Cave, China, revealed the evolution of the Asian summer monsoon (ASM) between 49.1 and 59.5 ka, and the δ18O values recorded Dansgaard/Oeschger (D/O) events 13–17. The Yangkou record shows a relatively gradual transition into the D/O 14 and 16 events. The discrepancy between the abrupt and gradual transitions of D/O 14 in the records from northern and southern China, respectively, suggests different responses of the ASM to climate changes in the high northern latitudes. The higher resolution δ18O record and more precise 230Th dating indicate that the timing of D/O 14 and 17 in the Hulu records at 53 and 58 ka should be shifted to 54.3 and 59 ka, respectively. The gradual strengthening of the ASM at the onsets of D/O 16 and 14 in our record is different from the abrupt temperature rise in the northern high latitudes. Some other factors must contribute to this relatively gradual ASM change in southern China, but the actual reason is still unknown.
With the rapid development of electronic information and technology, especially the explosive advance of novel electronic devices, ultra-wideband radar detector and satellite communication, the elimination of adverse electromagnetic waves (EWs) effectively is very necessary both for electronic safety and national defense security. As one of the important material basis for controlling adverse EW pollution, compatibility, shielding, and stealth capability of weaponry, microwave absorbing materials has long been an area of intense research activity. Graphene-based materials have attracted great interests for microwave absorption in recent years due to the unique structure and physicochemical properties of graphene, such as high specific surface area, ultrathin thickness, large interface, optical transmittance, and tunable conductive properties, etc. In this paper, the properties and absorption behavior of different kinds of microwave absorbing materials based on graphene were reviewed and discussed in detail. In addition, the perspective of the current challenges and key issues for achieving better microwave absorption performance of the graphene-based materials are provided.
The Lorentz factor (Γ) is an important parameter related to the relativistic jet physics. We study the evolution patterns of Γ within gamma-ray burst (GRB) and active galactic nuclear jets for individual GRB 090168, GRB 140508A, and 3C 454.3. By estimating the Γ values for well-separated pulses in GRBs 090618 and 140508A with an empirical relation derived from typical GRBs, we find that the Γ evolution pattern in the two GRBs are different. The increasing-to-coasting evolution pattern of Γ in GRB 090618 likely indicates that the GRB fireball is still being accelerated in the prompt phase. The clear decrease evolution pattern of Γ in GRB 140508A suggests the deceleration of the fireball components. By deriving the Γ value through fitting their spectral energy distribution in different flares of 3C 454.3, a pattern of Γ-tracking-γ-ray flux is clearly found, likely indicating that the observed gamma-ray flares are being due to the Doppler boosting effect to the jet emission.
A novel radio frequency identification tag antenna is composed of a resonant open-slot exciter and a dipole-type ground radiator. For a conjugate match to the Alien Higgs-4 chip impedance of 8−j149 Ω at 925 MHz, a quarter wavelength open-slot resonator embedded at the center of the dipole-type ground plane (130 × 18 mm2) was investigated and fabricated. Simple size adjustments and various loaded inductor of the open-slot resonator allow for easy control of the tag antenna resistance and inductive reactance, from which the chip impedance requirement can be easily obtained. The read range of the prototype antenna attached on a foam in the free space can reach more than 9 m, which has been tested for a radio frequency identification reader with 4.0-W of effective isotropic radiated power. Measurement data are in good agreement with simulation results.
In the foreland area of western Taiwan, some of the pre-orogenic basement-involved normal faults were reactivated during the subsequent compressional tectonics. The main purpose of this paper is to investigate the role played by the pre-existing normal faults in the recent tectonics of western Taiwan. In NW Taiwan, reactivated normal faults with a strike-slip component have developed by linkage of reactivated single pre-existing normal faults in the foreland basin and acted as transverse structures for low-angle thrusts in the outer fold-and-thrust belt. In the later stage of their development, the transverse structures were thrusted and appear underneath the low-angle thrusts or became tear faults in the inner fold-and-thrust belt. In SW Taiwan, where the foreland basin is lacking normal fault reactivation, the pre-existing normal faults passively acted as ramp for the low-angle thrusts in the inner fold-and-thrust belt. Some of the active faults in western Taiwan may also be related to reactivated normal faults with right-lateral slip component. Some main earthquake shocks related to either strike-slip or thrust fault plane solution occurred on reactivated normal faults, implying a relationship between the pre-existing normal fault and the triggering of the recent major earthquakes. Along-strike contrast in structural style of normal fault reactivation gives rise to different characteristics of the deformation front for different parts of the foreland area in western Taiwan. Variations in the degree of normal fault reactivation also provide some insights into the way the crust embedding the pre-existing normal faults deformed in response to orogenic contraction.
Average differences in children's language abilities by socioeconomic status (SES) emerge early in development and predict academic achievement. Previous research has focused on coarse-grained outcome measures such as vocabulary size, but less is known about the extent to which SES differences exist in children's strategies for comprehension and learning. We measured children's (N = 98) comprehension of passive sentences to investigate whether SES differences are more pronounced in overall knowledge of the construction or in more specific abilities to process sentences during real-time interpretation. SES differences in comprehension emerged when syntactic revision of passives was necessary, and disappeared when the need to revise was removed. Further, syntactic revision but not knowledge of the passive best explained the association between SES and a standardized measure of syntactic development. These results demonstrate that SES differences in syntactic development may result from how children recruit syntactic information within sentences.
We describe the development, pilot-testing, refinement, and four evaluations of Diagnostic Question Generator (DQGen), which automatically generates multiple choice cloze (fill-in-the-blank) questions to test children's comprehension while reading a given text. Unlike previous methods, DQGen tests comprehension not only of an individual sentence but of the context preceding it. To test different aspects of comprehension, DQGen generates three types of distractors: ungrammatical distractors test syntax; nonsensical distractors test semantics; and locally plausible distractors test inter-sentential processing.
(1) A pilot study of DQGen 2012 evaluated its overall questions and individual distractors, guiding its refinement into DQGen 2014.
(2) Twenty-four elementary students generated 200 responses to multiple choice cloze questions that DQGen 2014 generated from forty-eight stories. In 130 of the responses, the child chose the correct answer. We define the distractiveness of a distractor as the frequency with which students choose it over the correct answer. The incorrect responses were consistent with expected distractiveness: twenty-seven were plausible, twenty-two were nonsensical, fourteen were ungrammatical, and seven were null.
(3) To compare DQGen 2014 against DQGen 2012, five human judges categorized candidate choices without knowing their intended type or whether they were the correct answer or a distractor generated by DQGen 2012 or DQGen 2014. The percentage of distractors categorized as their intended type was significantly higher for DQGen 2014.
(4) We evaluated DQGen 2014 against human performance based on 1,486 similarly blind categorizations by twenty-seven judges of sixteen correct answers, forty-eight distractors generated by DQGen 2014, and 504 distractors authored by twenty-one humans. Surprisingly, DQGen 2014 did significantly better than humans at generating ungrammatical distractors and marginally better than humans at generating nonsensical distractors, albeit slightly worse at generating plausible distractors. Moreover, vetting DQGen 2014's output and writing distractors only when necessary would halve the time to write them all, and produce higher quality distractors.
A higher intake of fruits and vegetables (F&V) compared with animal-derived foods is associated with lower risks of all-cause-, cancer- and CVD-related mortalities. However, the association between consumption patterns and medical costs remains unclear. The effects of various food group costs on medical service utilisation and costs were investigated. The study cohort was recruited through the Elderly Nutrition and Health Survey in Taiwan between 1999 and 2000 and followed-up for 8 years until 2006. It comprised free-living elderly participants who provided a 24-h dietary recall. Daily energy-adjusted food group costs were estimated. Annual medical service utilisation and costs for 1445 participants aged 65–79 years were calculated from the National Health Insurance claim data. Generalised linear models were used to appraise the associations between the food group costs and medical service utilisation and costs. Older adults with the highest F&V cost tertile had significantly fewer hospital days (30 %) and total medical costs (19 %), whereas those in the highest animal-derived group had a higher number of hospital days (28 %) and costs (83 %) as well as total medical costs (38 %). Participants in the high F&V and low animal-derived cost groups had the shortest annual hospitalisation stays (5·78 d) and lowest costs (NT$38 600) as well as the lowest total medical costs (NT$75 800), a mean annual saving of NT$45 200/person. Older adults who spend more on F&V and less on animal-derived foods have a reduced medical-care system burden. This provides opportunities for nutritionally related healthcare system investment strategies.