Suppressed terahertz dynamics of water confined in nanometer gaps.

Nanoconfined waters exhibit low static permittivity mainly due to interfacial effects that span about one nanometer. The characteristic length scale may be much longer in the terahertz (THz) regime where long-range collective dynamics occur; however, the THz dynamics have been largely unexplored because of the lack of a robust platform. Here, we use metallic loop nanogaps to sharply enhance light-matter interactions and precisely measure real and imaginary THz refractive indices of nanoconfined water at gap widths ranging from 2 to 20 nanometers, spanning mostly interfacial waters all the way to quasi-bulk waters. We find that, in addition to the well-known interfacial effect, the confinement effect also contributes substantially to the decrease in the complex refractive indices of the nanoconfined water by cutting off low-energy vibrational modes, even at gap widths as large as 10 nanometers. Our findings provide valuable insights into the collective dynamics of water molecules which is crucial to understanding water-mediated processes.

Coherent Oscillations in a SrRuO3/BiFeO3 Superlattice.

We investigated the ultrafast dynamics of a SrRuO3/BiFeO3 superlattice grown on a SrTiO3 substrate using a near infrared pump-probe technique at various temperatures. The superlattice exhibits a ferromagnetic order inherited from the SrRuO3 layer. The pump-induced changes in the reflectivity reveal periodic oscillations. We found that the oscillation frequency can be well explained by zone-folded acoustic phonon oscillations, whose dispersion depends on the sound velocity, density, and thickness within the supercell of each constituent layer. It is found that the observed oscillation frequency corresponds to the A1 mode, which suggests that oscillations are excited due to pump-induced expansion of the SrRuO3 layer that absorbs the pump photon. Temperature-dependent measurements reveal significant suppression of the oscillation amplitude in the ferromagnetic state. The suppressed amplitude is proportional to the square of the magnetization, M(T)2. This phenomenon can be attributed to a strong magnetostriction effect of SrRuO3 that suppresses lattice expansion upon pumping.

Effects of Cognitive Inhibition Preceding Voluntary Step Responses to Visual Stimuli in Young and Older Adults.

OBJECTIVES: Age-related changes in executive functions, especially inhibitory control, correlate to decreased balance control and increased fall risk. However, only a few studies focused on the performance of tasks integrating balance and inhibitory control. This study aims to determine the effects of cognitive inhibition preceding the initiation of voluntary steps in young and older adults. METHODS: Performance of 3 stepping tasks (a Simon, Flanker, and a combined Simon-Flanker task [SFT]) were analyzed in 23 young adults and 43 older adults. Each task included congruent and incongruent trials in different step directions. Analyses focused on temporal aspects of step responses as identified by changes in Center of Pressure (CoP) and foot position. A 3-way repeated-measures ANOVA was used to evaluate "inhibition," "age," and "task" effects. RESULTS: With large effect sizes, "inhibition" as well as "age" resulted in longer durations of an initial preparatory phase as well as the step response phase. The SFT showed the largest "task" effects. Duration of CoP movement had the largest impact on total step execution in older adults. A significant interaction effect of "age*inhibition" was found on the duration of CoP movement, but not on CoP onset. DISCUSSION: Overall, our results demonstrate that cognitive inhibition has more impact in older adults, the longer duration of CoP movements in older adults may reflect an ineffective step preparation. Our examination of the duration of subsequent phases which comprise perceptual processing and conflict resolution, response initiation, and step execution sheds light on how cognitive inhibition affects voluntary stepping behavior in young and older adults.

A scoping review of voluntary gait adaptability tasks requiring cognitive demands in older adults.

PURPOSE: Voluntary gait adaptability is a complex construct that requires cognitive demands and dynamic balance control; it also has implications for the daily lives of older adults. This ability has been extensively studied, however, a comprehensive overview of appropriate tasks for measuring voluntary gait adaptability in older adults is lacking. Our scoping review aimed to identify existing voluntary gait adaptability tasks for older adults, summarize the specific methodological features requiring cognitive demands found in previous studies, and categorize these tasks according to experimental procedure and setup. METHODS: A comprehensive literature search was performed using six databases (PubMed, SPORTDiscus, Web of Science, CINAHL, MEDLINE, and Embase). This included studies that investigated voluntary gait adaptability in older adults (≥ 65 years old) with and without neurological disorders, with a focus on experimental tasks requiring cognitive function (e.g., response to visual or auditive stimuli) while walking. RESULTS: Sixteen studies were included; most involved visual stimuli, such as obstacles, stairs, or colored cues, and few required auditory stimuli. The studies were categorized according to the experimental procedure, for example, ascent/descent of obstacles (n = 3), inconsistent surfaces (n = 1), lateral gait adjustment (n = 4), obstacle avoidance (n = 6), and stepping tasks (n = 2), as well as experimental setup, including instrumented treadmills (n = 3), stairs (n = 3), and walkways (n = 10). CONCLUSION: The results show wide heterogeneity between studies regarding experimental procedures and setup. Our scoping review highlights the need for additional experimental studies and systematic reviews on voluntary gait adaptability in older adults.

Age-related effects of repeated task switching in a novel voluntary gait adaptability task.

Age-related effects of task switching have been extensively studied based on cognitive tasks and simple motor tasks, but less on complex cognitive-motor tasks involving dynamic balance control while walking. The latter tasks may especially be difficult and relevant for older adults in terms of safe mobility in daily life. The aim of the present study was, therefore, to examine age-related changes in task-switching adaptability using a novel voluntary gait adaptability test protocol. Fifteen healthy young (27.5 ± 2.9 years) and 16 healthy old (70.9 ± 7.6 years) adults carried out 2 different visual target stepping tasks (either target avoidance or stepping) twice in a block (A-B-A-B, 2 min per task; three blocks in total) without any intrablock breaks. Our results showed that old adults showed significantly more step errors both in Tasks A and B as well as more interference effects than young adults. Age-related differences in step accuracy were significant in the anterior-posterior direction both in Task A and B but not in the mediolateral direction. Both in step errors and accuracy, no interaction effects of age and trial were shown. Our results suggest that old adults could not cope with rapid and direct task changes in our voluntary gait adaptability task as young adults. Since the significant main effect of trial for Task B, but not Task A appears to be due to different task complexity, further studies may determine the effect of task complexity or task switch timing.

Keldysh Space Control of Charge Dynamics in a Strongly Driven Mott Insulator.

The fate of a Mott insulator under strong low frequency optical driving conditions is a fundamental problem in quantum many-body dynamics. Using ultrafast broadband optical spectroscopy, we measured the transient electronic structure and charge dynamics of an off-resonantly pumped Mott insulator Ca_{2}RuO_{4}. We observe coherent bandwidth renormalization and nonlinear doublon-holon pair production occurring in rapid succession within a sub-100-fs pump pulse duration. By sweeping the electric field amplitude, we demonstrate continuous bandwidth tuning and a Keldysh crossover from a multiphoton absorption to quantum tunneling dominated pair production regime. Our results provide a procedure to control coherent and nonlinear heating processes in Mott insulators, facilitating the discovery of novel out-of-equilibrium phenomena in strongly correlated systems.

Effects of practice on visuo-spatial attention in a wayfinding task.

Several studies have evaluated the distribution of visuo-spatial attention in a wayfinding task, using gaze direction as an indicator for the locus of attention. We extended that work by evaluating how visuo-spatial attention is modified by wayfinding practice. Young and older participants followed prescribed routes through a virtual city on six trials. Each trial was followed by a route recall test, where participants saw screenshots of intersections encountered, and had to indicate which way to proceed. Behavioral and gaze data were registered in those tests. Wayfinding accuracy increased from trial to trial, more so in young than in older persons. Total gaze time, mean fixation time, and the vertical scatter of fixations decreased from trial to trial, similarly in young and older persons. The horizontal scatter of fixations did not differ between trials and age groups. The incidence of fixations on the subsequently chosen side also did not differ between trials, but it increased in older age. We interpret these findings as evidence that as wayfinding practice increased, participants gradually narrowed their attentional focus to the most relevant screenshot area, processed information within this focus more efficiently, reduced the total time in which attention dwelled on the rejected side of the screenshot, but maintained the total time on the chosen side. These dynamic changes of visuo-spatial attention were comparable in young and older participants. However, it appears that decision-making differed between age groups: older persons' attention dwelled longer on the chosen side before they made their choice.

Eye-Head-Trunk Coordination While Walking and Turning in a Simulated Grocery Shopping Task.

Previous studies argued that body turns are executed in an ordered sequence: the eyes turn first, followed by the head and then by the trunk. The purpose of this study was to find out whether this sequence holds even if body turns are not explicitly instructed, but nevertheless are necessary to reach an instructed distal goal. We asked participants to shop for grocery products in a simulated supermarket. To retrieve each product, they had to walk down and aisle, and then turn left or right into a corridor that led towards the target shelf. The need to make a turn was never mentioned by the experimenter, but it nevertheless was required in order to approach the target shelf. Main variables of interest were the delay between eye and head turns towards the target shelf, as well as the delay between head and trunk turns towards the target shelf. We found that both delays were consistently positive, and that their magnitude was near the top of the range reported in literature. We conclude that the ordered sequence of eye - then head - then trunk turns can be observed not only with a proximal, but also with a distal goal.

Acquisition of landmark, route, and survey knowledge in a wayfinding task: in stages or in parallel?

According to an influential concept, humans acquire spatial knowledge about their environment in three distinct stages: landmark knowledge is acquired first, then route knowledge, and finally survey knowledge. The stage concept has been challenged by studies which observed that in a wayfinding paradigm, route, and survey knowledge emerge at the same time and; therefore, were seemingly acquired in parallel. However, this experimental evidence is not conclusive because the above studies suffered from a ceiling effect. The present study was designed to overcome the ceiling effect by increasing the complexity of the wayfinding task. We asked 60 young participants to find their way through an urban environment rendered in virtual reality, and assessed their landmark, route, and survey knowledge after each of ten trials. We found that all three types of knowledge gradually increased from the first to the last trial. We further found that correlations between the three types of knowledge increased from trial to trial. This outcome disagrees profoundly with the stage concept, but is compatible with the parallel concept. Specifically, it is in accordance with the view that landmark, route, and survey knowledge are acquired by multiple overlapping and interacting processes: those processes may start out more or less independently in the first trial but, due to common constraints or synergies, may gradually increase their cooperation during subsequent trials.

Ecological validity of manual grasping movements in an everyday-like grocery shopping task.

In our earlier research, kinematic and kinetic parameters of grasping differed significantly when participants grasped the same object once in a traditional laboratory paradigm, and once as part of a captivating computer game. We attributed this finding to the fact that grasping movements in the laboratory were repetitive and meaningless, while those in the computer game were embedded in complex behavior and served a meaningful purpose. In that work, we argued that grasping in the computer game is more characteristic of everyday life behavior; however, this conclusion has been criticized on the grounds that a computer game is not a typical everyday activity. The present study therefore compares grasping in a traditional laboratory paradigm to that in an indisputably everyday context: grocery shopping. Thirty-three young adults executed externally triggered arm movements to grasp nondescript objects (laboratory task, L) and place them on a tablet, or they walked through a fictitious grocery store towards a shelf to grasp grocery products and placed them into a shopping basket (everyday-like task, E). Size, shape, weight and location of to-be-grasped objects were identical in both tasks. We found that of the analyzed 16 kinematic parameters, 13 differed significantly between tasks. Specifically, grip apertures were larger, movements were slower and grip-transport coupling was more variable in E compared to L. We conclude that kinematic differences between both persist even if task is more realistic than in our earlier research. Our findings are compatible with the notion that movement planning is less stringent in E than in L.

A novel fabrication method for the nanoscale tunneling field effect transistor.

Tunneling Field Effect Transistors (TFETs) are considered as a candidate for low power applications. However, most of TFETs have been researched on only for long channels due to the misalignment problem that occurs during the source/drain doping process in device fabrication. Thus, a new method is proposed for the fabrication of TFETs in nanoscale regions. This proposed fabrication process does not need an additional mask to define the source/drain regions, and makes it possible to form a self-aligned source/drain doping process. In addition, through TCAD simulation, the electrical characteristics of a TFET with dopant engineering and a rounded gate edge shape for a higher on/off current ratio were investigated. As a result, the TFET showed the properties of a larger on-current, a lower average subthreshold swing (58.5 mV/dec), and a 30-fold smaller leakage current compared to the conventional TFET The TFET with dopant engineering and a rounded gate edge shape can also be fabricated simply through the proposed fabrication process.

Single electron transistor with P-type sidewall spacer gates.

A single-electron transistor (SET) is one of the promising solutions to overcome the scaling limit of the Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). Up to now, various kinds of SETs are being proposed and SETs with a dual gate (DG) structure using an electrical potential barrier have been demonstrated for room temperature operation. To operate DG-SETs, however, extra bias of side gates is necessary. It causes new problems that the electrode for side gates and the extra bias for electrical barrier increase the complexity in circuit design and operation power consumption, respectively. For the reason, a new mechanism using work function (WF) difference is applied to operate a SET at room temperature by three electrodes. Its structure consists of an undoped active region, a control gate, n-doped source/drain electrodes, and metal/silicide or p-type silicon side gates, and a SET with metal/silicide gates or p-type silicon gates forms tunnel barriers induced by work function between an undoped channel and grounded side gates. Via simulation, the effectiveness of the new mechanism is confirmed through various silicide materials that have different WF values. Furthermore, by considering the realistic conditions of the fabrication process, SET with p-type sidewall spacer gates was designed, and its brief fabrication process was introduced. The characteristics of its electrical barrier and the controllability of its control gate were also confirmed via simulation. Finally, a single-hole transistor with n-type sidewall spacer gates was designed.