Thermo-Compression Bonding of Cu/SnAg Pillar Bumps with Electroless Palladium Immersion Gold (EPIG) Surface Finish.

Thermo-compression bonding (TCB) properties of Cu/SnAg pillar bumps on electroless palladium immersion gold (EPIG) were evaluated in this study. A test chip with Cu/SnAg pillar bumps was bonded on the surface-finished Cu pads with the TCB method. The surface roughness of the EPIG was 82 nm, which was 1.6 times higher than that of the ENEPIG surface finish because the EPIG was so thin that it could not flatten rough bare Cu pads. From the cross-sectional SEM micrographs, the filler trapping of the TC-bonded EPIG was much higher than that of the ENEPIG sample. The high filler trapping of the EPIG sample was due to the high surface roughness of the EPIG surface finish. The contact resistance increased as the thermal cycle time increased. The increase of the contact resistance with 1500 cycles of the thermal cycle test was 26% higher for the EPIG sample than for the ENEPIG sample.

Hippocampal Neuronal Activity Preceding Stimulus Predicts Later Memory Success.

Hippocampal neuronal activity at a time preceding stimulus onset affects episodic memory performance. We hypothesized that neuronal activity preceding an event supports successful memory formation; therefore, we explored whether a characterized encoding-associated brain activity, viz. the neuronal activity preceding a stimulus, predicts subsequent memory formation. To address this issue, we assessed the activity of single neurons recorded from the hippocampus in humans, while participants performed word memory tasks. Human hippocampal single-unit activity elicited by a fixation cue preceding words increased the firing rates (FRs) and predicted whether the words are recalled in a subsequent memory test; this indicated that successful memory formation in humans can be predicted by a preceding stimulus activity during encoding. However, the predictive effect of preceding stimulus activity did not occur during retrieval. These findings suggest that the preparative arrangement of brain activity before stimulus encoding improves subsequent memory performance.

Enhancement of dielectric performance of encapsulation in barium titanate oxide using size-controlled reduced graphene oxide.

Ferroelectric barium titanate (BTO) powder particles were encapsulated by three different sizes of reduced graphene oxide (rGO) platelets. The size of the graphene oxide (GO) platelets is controlled by varying the horn type ultrasonic times, i.e. 0, 30, and 60 min, respectively, and they are reduced with hydrazine to obtain rGO-encapsulated BTO (rGO@BTO) film. The rGO@BTO film exhibits an increase in the dielectric characteristics due to the interfacial polarization. These improved characteristics include a dielectric constant of 194 (a large increment of 111%), along with the dielectric loss of 0.053 (a slight increment of 13%) at 1 kHz, compared to the pure BTO dielectric film. The improvement in the dielectric constant of the rGO@BTO is attributed to the encapsulation degree between the rGO platelets and BTO powder particles, which results in the interfacial polarization and micro-capacitor effect in a dielectric film, and also contributes to a low dielectric loss. Therefore, a suitable size of rGO platelets for encapsulation is essential for high-dielectric performance.

Fronto-parietal single-trial brain connectivity benefits successful memory recognition.

Successful recognition has been known to produce distinct patterns of neural activity. Many studies have used spectral power or event-related potentials of single recognition-specific regions as classification features. However, this does not accurately reflect the mechanisms behind recognition, in that recognition requires multiple brain regions to work together. Hence, classification accuracy of subsequent memory performance could be improved by using functional connectivity within memory-related brain networks instead of using local brain activity as classifiers. In this study, we examined electroencephalography (EEG) signals while performing a word recognition memory task. Recorded EEG signals were collected using a 32-channel cap. Connectivity measures related to the left hemispheric fronto-parietal connectivity (P3 and F3) were found to contribute to the accurate recognition of previously studied memory items. Classification of subsequent memory outcome using connectivity features revealed that the classifier with support vector machine achieved the highest classification accuracy of 86.79 ± 5.93% (mean ± standard deviation) by using theta (3-8 Hz) connectivity during successful recognition trials. The results strongly suggest that highly accurate classification of subsequent memory outcome can be achieved by using single-trial functional connectivity.

Does Motor Tract Integrity at 1 Month Predict Gait and Balance Outcomes at 6 Months in Stroke Patients?

Recovery of balance and gait ability is important in stroke patients. Several studies have examined the role of white matter tracts in the recovery of gait and balance, but the results have been inconclusive. Therefore, we examined whether the integrity of the corticospinal tract (CST), corticoreticular pathway (CRP), and cortico-ponto-cerebellar tract (CPCT) at 1 month predicted balance and gait function 6 months after stroke onset. This retrospective longitudinal observational clinical study assessed 27 patients with first-ever unilateral supratentorial stroke. The subjects underwent diffusion tensor imaging 1 month after the stroke, and the Functional Ambulation Categories (FAC) and Berg Balance Scale (BBS) scores were assessed after 6 months. The normalized fiber number (FN) and fractional anisotropy (FA) results for the CST, CRP and CPCT were also obtained. The FN and FA results for the CST, CRP, or CPCT at 1 month were not related to the gait or balance at 6 months. There was also no difference in FAC values at 1 month after stoke onset among three groups differing in degree of independence of ambulation. The integrity of the CST, CRP, and CPCT on 1 month after stroke onset was not associated with gait or balance after 6 months. The white matter integrity did not predict the clinical outcome.

Gender bias in academia: A lifetime problem that needs solutions.

Despite increased awareness of the lack of gender equity in academia and a growing number of initiatives to address issues of diversity, change is slow, and inequalities remain. A major source of inequity is gender bias, which has a substantial negative impact on the careers, work-life balance, and mental health of underrepresented groups in science. Here, we argue that gender bias is not a single problem but manifests as a collection of distinct issues that impact researchers' lives. We disentangle these facets and propose concrete solutions that can be adopted by individuals, academic institutions, and society.

Prediction of Successful Memory Encoding Based on Lateral Temporal Cortical Gamma Power.

Prediction of successful memory encoding is important for learning. High-frequency activity (HFA), such as gamma frequency activity (30-150 Hz) of cortical oscillations, is induced during memory tasks and is thought to reflect underlying neuronal processes. Previous studies have demonstrated that medio-temporal electrophysiological characteristics are related to memory formation, but the effects of neocortical neural activity remain underexplored. The main aim of the present study was to evaluate the ability of gamma activity in human electrocorticography (ECoG) signals to differentiate memory processes into remembered and forgotten memories. A support vector machine (SVM) was employed, and ECoG recordings were collected from six subjects during verbal memory recognition task performance. Two-class classification using an SVM was performed to predict subsequently remembered vs. forgotten trials based on individually selected frequencies (low gamma, 30-60 Hz; high gamma, 60-150 Hz) at time points during pre- and during stimulus intervals. The SVM classifier distinguished memory performance between remembered and forgotten trials with a mean maximum accuracy of 87.5% using temporal cortical gamma activity during the 0- to 1-s interval. Our results support the functional relevance of ECoG for memory formation and suggest that lateral temporal cortical HFA may be utilized for memory prediction.

Plasma Polymerized SiCOH Films from Octamethylcyclotetrasiloxane by Dual Radio Frequency Inductively Coupled Plasma Chemical Vapor Deposition System.

We have fabricated porous plasma polymerized SiCOH (ppSiCOH) films with low-dielectric constants (low-k, less than 2.9), by applying dual radio frequency plasma in inductively coupled plasma chemical vapor deposition (ICP-CVD) system. We varied the power of the low radio frequency (LF) of 370 kHz from 0 to 65 W, while fixing the power of the radio frequency (RF) of 13.56 MHz. Although the ppSiCOH thin film without LF had the lowest k value, its mechanical strength is not high to stand the subsequent semiconductor processing. As the power of the LF was increased, the densities of ppSiCOH films became high, accordingly high in the hardness and elastic modulus, with quite satisfactory low-k value of 2.87. Especially, the ppSiCOH film, deposited at 35 W, exhibited the highest mechanical strength (hardness: 1.7 GPa, and elastic modulus: 9.7 GPa), which was explained by Fourier transform infrared spectroscopy. Since the low-k material is widely used as an inter-layer dielectric insulator, good mechanical properties are required to withstand chemical mechanical polishing damage. Therefore, we suggest that plasma polymerized process based on the dual frequency can be a good candidate for the deposition of low-k ppSiCOH films with enhanced mechanical strength.

Characterization of Bilayer Organic Solar Cells with Carbon Nanotubes Using Impedance Analysis.

Four organic solar cell (OSC) devices with the bilayer heterojunction architecture were investigated, where carbon nanotubes (CNTs) were doped within the acceptor layer. The power conversion efficiency (PCE) of the CNT-incorporated device with a concentration of 0.004 wt% is approximately 20% point higher than that of the reference one. As the concentration of CNTs became higher, the PCE of the devices deteriorated; this could be caused by the percolative connection of CNTs within the layer. The voltage dependence on the effective lifetime of the charge carriers, determined by Cole-Cole curves of the impedance analysis, was different for the reference and CNT-incorporating devices-the lifetime of the CNT-incorporated ones was shorter, possibly owing to the high local electric field near the CNTs. Controlling the concentration of CNTs below the critical concentration of percolation is a key factor in achieving high photovoltaic performance.

Task-dependent effects of intracranial hippocampal stimulation on human memory and hippocampal theta power.

BACKGROUND: Despite its potential to revolutionize the treatment of memory dysfunction, the efficacy of direct electrical hippocampal stimulation for memory performance has not yet been well characterized. One of the main challenges to cross-study comparison in this area of research is the diversity of the cognitive tasks used to measure memory performance. OBJECTIVE: We hypothesized that the tasks that differentially engage the hippocampus may be differentially influenced by hippocampal stimulation and the behavioral effects would be related to the underlying hippocampal activity. METHODS: To investigate this issue, we recorded intracranial EEG from and directly applied stimulation to the hippocampus of 10 epilepsy patients while they performed two different verbal memory tasks - a word pair associative memory task and a single item memory task. RESULTS: Hippocampal stimulation modulated memory performance in a task-dependent manner, improving associative memory performance, while impairing item memory performance. In addition, subjects with poorer baseline cognitive function improved much more with stimulation. iEEG recordings from the hippocampus during non-stimulation encoding blocks revealed that the associative memory task elicited stronger theta oscillations than did item memory and that stronger theta power was related to memory performance. CONCLUSIONS: We show here for the first time that stimulation-induced associative memory enhancement was linked to increased theta power during retrieval. These results suggest that hippocampal stimulation enhances associative memory but not item memory because it engages more hippocampal theta activity and that, in general, increasing hippocampal theta may provide a neural mechanism for successful memory enhancement.

Direct Stimulation of Human Hippocampus During Verbal Associative Encoding Enhances Subsequent Memory Recollection.

Previous studies have reported conflicting results regarding the effect of direct electrical stimulation of the human hippocampus on memory performance. A major function of the hippocampus is to form associations between individual elements of experience. However, the effect of direct hippocampal stimulation on associative memory remains largely inconclusive, with most evidence coming from studies employing non-invasive stimulation. Here, we therefore tested the hypothesis that direct electrical stimulation of the hippocampus specifically enhances hippocampal-dependent associative memory. To test this hypothesis, we recruited surgical patients with implanted subdural electrodes to perform a word pair memory task during which the hippocampus was stimulated. Our results indicate that stimulation of the hippocampus during encoding helped to build strong associative memories and enhanced recollection in subsequent trials. Moreover, stimulation significantly increased theta power in the lateral middle temporal cortex during successful memory encoding. Overall, our findings indicate that hippocampal stimulation positively impacts performance during a word pair memory task, suggesting that successful memory encoding involves the temporal cortex, which may act together with the hippocampus.