Optomechanical and Crystallization Phenomena Visualized with 4D Electron Microscopy: Interfacial Carbon Nanotubes on Silicon Nitride

With ultrafast electron microscopy (UEM), we report observation of the nanoscopic crystallization of amorphous silicon nitride, and the ultrashort optomechanical motion of the crystalline silicon nitride at the interface of an adhering carbon nanotube network. The in situ static crystallization of the silicon nitride occurs only in the presence of an adhering nanotube network, thus indicating their mediating role in reaching temperatures close to 1000 °C when exposed to a train of laser pulses. Under such condition, 4D visualization of the optomechanical motion of the specimen was followed by quantifying the change in diffraction contrast of crystalline silicon nitride, to which the nanotube network is bonded. The direction of the motion was established from a tilt series correlating the change in displacement with both the tilt angle and the response time. Correlation of nanoscopic motion with the picosecond atomic-scale dynamics suggests that electronic processes initiated in the nanotubes are responsible for the initial ultrafast optomechanical motion. The time scales accessible to UEM are 12 orders of magnitude shorter than those traditionally used to study the optomechanical motion of carbon nanotube networks, thus allowing for distinctions between the different electronic and thermal mechanisms to be made

Nanofriction Visualized in Space and Time by 4D Electron Microscopy

In this letter, we report a novel method of visualizing nanoscale friction in space and time using ultrafast electron microscopy (UEM). The methodology is demonstrated for a nanoscale movement of a single crystal beam on a thin amorphous membrane of silicon nitride. The movement results from the elongation of the crystal beam, which is initiated by a laser (clocking) pulse, and we examined two types of beams: those that are free of friction and the others which are fixed on the substrate. From observations of image change with time we are able to decipher the nature of microscopic friction at the solid−solid interface: smooth-sliding and periodic slip-stick friction. At the molecular and nanoscale level, and when a force parallel to the surface (expansion of the beam) is applied, the force of gravity as a (perpendicular) load cannot explain the observed friction. An additional effective load being 6 orders of magnitude larger than that due to gravity is attributed to Coulombic/van der Waals adhesion at the interface. For the case under study, metal−organic crystals, the gravitational force is on the order of piconewtons whereas the static friction force is 0.5 μN and dynamic friction is 0.4 μN; typical beam expansions are 50 nm/nJ for the free beam and 10 nm/nJ for the fixed beam. The method reported here should have applications for other materials, and for elucidating the origin of periodic and chaotic friction and their relevance to the efficacy of nano(micro)-scale devices

Irreversible Chemical Reactions Visualized in Space and Time with 4D Electron Microscopy

We report direct visualization of irreversible chemical reactions in space and time with 4D electron microscopy. Specifically, transient structures are imaged following electron transfer in copper-tetracyanoquinodimethane [Cu(TCNQ)] crystals, and the oxidation/reduction process, which is irreversible, is elucidated using the single-shot operation mode of the microscope. We observed the fast, initial structural rearrangement due to Cu^+ reduction and the slower growth of metallic Cu^0 nanocrystals (Ostwald ripening) following initiation of the reaction with a pulse of visible light. The mechanism involves electron transfer from TCNQ anion-radical to Cu^+, morphological changes, and thermally driven growth of discrete Cu^0 nanocrystals embedded in an amorphous carbon skeleton of TCNQ. This in situ visualization of structures during reactions should be extendable to other classes of reactive systems

The Economic Structure of the Firm

Considerable effort has been channelled into theoretical investigations of the structure of the firm over the past several years. Most of the new work has been produced by economists. Lawyers have been content simply to draw upon the economic arguments, often in an uncritical way. The author examines the various economic models and identifies their shared dependence on the significance of an actors\u27 control over the employment of assets. The control proposition is then further developed in the course of the construction of a general model focussing on the production unit

Gender Impact on Trauma-Exposed Populations

Gender differences in trauma exposure have been well-established in published research. This paper explored the relationship between gender and its impact on exposure to traumatic events and the outcomes within trauma-exposed populations. Trauma can have profound and lasting effects on physical, mental, social, and behavioral well-being. The literature review identified gender differences in exposure to trauma types, PTSD prevalence and symptomatology, other mental health disorders, behavioral outcomes, and differences in physical health. Additionally, it explored the role of support systems, coping mechanisms, and risk factors for particular trauma-related outcomes. Furthermore, this paper examined the implications of the findings for professional practice and future research. The problem has been significant in the field of education as teachers need to understand the effects of trauma and how to meet the needs of students to help them recover and learn. Through thorough analysis of existing research, there has been an overwhelming disparity of studies on trauma-exposed women. The synthesis of this collection of research created a better understanding of the outlined differences in trauma exposure and outcomes by gender but also highlighted the need for gender-sensitive approaches to research and professional practice. The insights gained from the studies emphasized the need to create interventions and policies to mitigate the effects of trauma differences by gender. Keywords: trauma, posttraumatic stress disorder (PTSD), outcomes, gender differences, adverse childhood experiences (ACEs

The Extent and Effects of an Ecological Invasion

America has a people who are on the move. Modern transportation, communication, decentralization of industry, and crowding of cities have all encouraged a mobile population. In this mobility, all cities include within their boundaries definite characteristics of many neighborhoods. Sociologists by concensus of opinion define a neighborhood as an area with fairly well-defined boundaries, occupied by individuals or families living in close physical proximity. From a social-psychological point of view, the emphasis would be upon the attitudes of neighbors toward each other and of the emotional intensity of the interaction. The specific area selected as the basis for this study was a cluster of neighborhoods which were in the process of under going many changes both socially and economically by the invasion of the Negro group. Because of the marked change by Invasion and succession recently brought about through mobility of population, social planning interest has been directed toward a means of meeting some of the basic needs of its population

Coordination Matters : Interpersonal Synchrony Influences Collaborative Problem-Solving

The authors thank Martha von Werthern and Caitlin Taylor for their assistance with data collection, Cathy Macpherson for her assistance with the preparation of the manuscript, and Mike Richardson, Alex Paxton, and Rick Dale for providing MATLAB code to assist with data analysis. The research was funded by the British Academy (SG131613).Peer reviewedPublisher PD

Thriving in a broken system : an ecological investigation of academic achievement and resilience in foster youth

Foster youth experience many adverse educational outcomes as a result of their frequently changing home and school environments. A well rounded model that identifies areas of resilience for foster youth may bolster the academic strengths of these adolescents and help them achieve academic success. With these needs in mind, this dissertation employed an ecological approach to fill the gaps in current knowledge of factors that influence academic achievement for foster youth. This secondary data analysis study utilized structural equation modeling (SEM) to create a holistic view of academic resilience that was based on Spencer’s 1995 Phenomenological Variant of Ecological Systems Theory (PVEST), using data from the National Survey of Child and Adolescent Well Being (NSCAW). The study determined what factors predicted academic achievement in foster youth, how development influenced achievement, and which factors most strongly predicted growth in achievement. Results indicated that relationships with caregivers and other supportive adults and activities that cultivate resilience among foster youth were important predictors of math and reading achievement. Age also played a role as early adolescents (ages 11-13) and mid adolescents (ages 14-17) differed in how well constructs within the presented models were measured for each group. Additionally, age and maladaptive coping predicted variability in the initial levels and growth in reading and math achievement. Implications for supporting academic resilience by reducing school mobility and developing partnerships with key community members were discussed.Educational Psycholog