A major reason for dental resin composite restoration replacement is related to secondary caries promoted by acid production from bacteria including Streptococcus mutans (S. mutans). We hypothesized ...that S. mutans has esterase activities that degrade dental resin composites and adhesives. Standardized specimens of resin composite (Z250), total-etch (Scotchbond Multipurpose, SB), and self-etch (Easybond, EB) adhesives were incubated with S. mutans UA159 or uninoculated culture medium (control) for up to 30 days. Quantification of the BisGMA-derived biodegradation by-product, bishydroxy-propoxy-phenyl-propane (BisHPPP), was performed by high-performance liquid chromatography. Surface analysis of the specimens was performed by scanning electron microscopy (SEM). S. mutans was shown to have esterase activities in levels comparable with those found in human saliva. A trend of increasing BisHPPP release throughout the incubation period was observed for all materials and was more elevated in the presence of bacteria vs. control medium for EB and Z250, but not for SB (p < .05). SEM confirmed the increased degradation of all materials with S. mutans UA159 vs. control. S. mutans has esterase activities at levels that degrade resin composites and adhesives; degree of degradation was dependent on the material’s chemical formulation. This finding suggests that the resin-dentin interface could be compromised by oral bacteria that contribute to the progression of secondary caries.
Small-Diameter Silicon Nanowire Surfaces Ma, D. D. D.; Lee, C. S.; Au, F. C. K. ...
Science (American Association for the Advancement of Science),
03/2003, Letnik:
299, Številka:
5614
Journal Article
Recenzirano
Small-diameter (1 to 7 nanometers) silicon nanowires (SiNWs) were prepared, and their surfaces were removed of oxide and terminated with hydrogen by a hydrofluoric acid dip. Scanning tunneling ...microscopy (STM) of these SiNWs, performed both in air and in ultrahigh vacuum, revealed atomically resolved images that can be interpreted as hydrogen-terminated Si (111)-(1 x 1) and Si (001)-(1 x 1) surfaces corresponding to$SiH_3$on Si (111) and$SiH_2$on Si (001), respectively. These hydrogen-terminated SiNW surfaces seem to be more oxidation-resistant than regular silicon wafer surfaces, because atomically resolved STM images of SiNWs were obtained in air after several days' exposure to the ambient environment. Scanning tunneling spectroscopy measurements were performed on the oxide-removed SiNWs and were used to evaluate the electronic energy gaps. The energy gaps were found to increase with decreasing SiNW diameter from 1.1 electron volts for 7 nanometers to 3.5 electron volts for 1.3 nanometers, in agreement with previous theoretical predictions.
Surgery is an important treatment modality for the majority of solid organ cancers. Unfortunately, cancer recurrence following surgery of curative intent is common, and typically results in ...refractory disease and patient death. Surgery and other perioperative interventions induce a biological state conducive to the survival and growth of residual cancer cells released from the primary tumour intraoperatively, which may influence the risk of a subsequent metastatic disease. Evidence is accumulating that anaesthetic and analgesic interventions could affect many of these pathophysiological processes, influencing risk of cancer recurrence in either a beneficial or detrimental way. Much of this evidence is from experimental in vitro and in vivo models, with clinical evidence largely limited to retrospective observational studies or post hoc analysis of RCTs originally designed to evaluate non-cancer outcomes. This narrative review summarises the current state of evidence regarding the potential effect of perioperative anaesthetic and analgesic interventions on cancer biology and clinical outcomes. Proving a causal link will require data from prospective RCTs with oncological outcomes as primary endpoints, a number of which will report in the coming years. Until then, there is insufficient evidence to recommend any particular anaesthetic or analgesic technique for patients undergoing tumour resection surgery on the basis that it might alter the risk of recurrence or metastasis.
Abstract
Understanding the competition between superconductivity and other ordered states (such as antiferromagnetic or charge-density-wave (CDW) state) is a central issue in condensed matter ...physics. The recently discovered layered kagome metal
A
V
3
Sb
5
(
A
= K, Rb, and Cs) provides us a new playground to study the interplay of superconductivity and CDW state by involving nontrivial topology of band structures. Here, we conduct high-pressure electrical transport and magnetic susceptibility measurements to study CsV
3
Sb
5
with the highest
T
c
of 2.7 K in
A
V
3
Sb
5
family. While the CDW transition is monotonically suppressed by pressure, superconductivity is enhanced with increasing pressure up to P1 ≈ 0.7 GPa, then an unexpected suppression on superconductivity happens until pressure around 1.1 GPa, after that,
T
c
is enhanced with increasing pressure again. The CDW is completely suppressed at a critical pressure P2 ≈ 2 GPa together with a maximum
T
c
of about 8 K. In contrast to a common dome-like behavior, the pressure-dependent
T
c
shows an unexpected double-peak behavior. The unusual suppression of
T
c
at P1 is concomitant with the rapidly damping of quantum oscillations, sudden enhancement of the residual resistivity and rapid decrease of magnetoresistance. Our discoveries indicate an unusual competition between superconductivity and CDW state in pressurized kagome lattice.
The microstructure-mechanical property relationships of a non-equiatomic FeMnCoCr high entropy alloy (HEA), which shows a single face-centered cubic (fcc) structure in the undeformed state, have been ...systematically investigated at room and cryogenic temperatures. Both strength and ductility increase significantly when reducing the probing temperature from 293 K to 77 K. During tensile deformation at 293 K, dislocation slip and mechanical twinning prevail. At 173 K deformation-driven athermal transformation from the fcc phase to the hexagonal close-packed (hcp) martensite is the dominant mechanism while mechanical twinning occurs in grains with high Schmid factors. At 77 K athermal martensitic transformation continues to prevail in addition to dislocation slip and twinning. The reduction in the mean free path for dislocation slip through the fine martensite bundles and deformation twins leads to the further increased strength. The joint activation of transformation and twinning under cryogenic conditions is attributed to the decreased stacking fault energy and the enhanced flow stress of the fcc matrix with decreasing temperature. These mechanisms lead to an elevated strain hardening capacity and an enhanced strength-ductility combination. The temperature-dependent synergy effects of martensite formation, twinning and dislocation plasticity originate from the metastability alloy design concept. This is realized by relaxing the equiatomic HEA constraints towards reduced Ni and increased Mn contents, enabling a non-equiatomic material with low stacking fault energy. These insights are important for designing strong and ductile Ni-saving alloys for cryogenic applications.
To unlock the full potential of monolithic gallium nitride (GaN) power integrated circuits, this article explores the feasibility of developing efficient and reliable on-chip gate driving and level ...shifting solutions, which fundamentally facilitate the on-chip implementation of GaN power circuits. As results, a self-bootstrapped hybrid (SBH) gate driving scheme and its circuitry are developed, which achieve rail-to-rail dynamic gate driving in normal operation and robust static gate driving in large transient moments. Meanwhile, an auto-lock auto-break (A2) level shifting technique is proposed to convert the gate driving control signals from low-voltage (LV) to high-voltage (HV) domains, without requiring any p-type devices. This enables the on-chip operation of high-side power switches and makes synchronous rectification possible. On-chip temperature sensing is implemented to monitor junction temperature directly at low circuit complexity and power and cost overheads, facilitating thermal protection at high power density. Furthermore, on-die dead-time control is presented to optimize zero voltage switching (ZVS) for high efficiency. All the techniques and circuits are demonstrated in a monolithic asymmetrical half-bridge (AHB) power converter on a GaN-on-SOI process. It achieves direct 48V/1V dc-dc conversion with a maximum load current of 5 A and a current density of 1.1 A/mm2. Among the existing monolithic GaN power ICs capable of on-chip synchronous rectification, it achieves the shortest rising- and falling-edge gate driving delays of 11.6 and 14.0 ns. Despite running doubled numbers of on-chip power transistors and gate drivers, it only consumes 70-mW static power.
This article presents a new power converter capable of direct 48-V/1-V dc-dc conversion with high efficiency. The proposed three-path four-state (3P4S) hybrid switching power stage enables high ...switching frequency (<inline-formula> <tex-math notation="LaTeX">f_{\mathrm {SW}} </tex-math></inline-formula>) operation and minimizes power passives by significantly reducing power switch voltage stress. To address the issues of power delivery path imbalances and potential device breakdown, an adaptive flying capacitor voltage (<inline-formula> <tex-math notation="LaTeX">V_{\mathrm {CF}} </tex-math></inline-formula>) rebalancing technique is introduced that improves design robustness and eliminates the need for direct floating <inline-formula> <tex-math notation="LaTeX">V_{\mathrm {CF}} </tex-math></inline-formula> sensing. Additionally, a dual-edge deadtime (<inline-formula> <tex-math notation="LaTeX">t_{\mathrm {dead}} </tex-math></inline-formula>) modulation with elastic <inline-formula> <tex-math notation="LaTeX">t_{\mathrm {dead}} </tex-math></inline-formula> control at switching nodes optimizes converter efficiency across different input voltage and load conditions. An IC prototype of the design was fabricated and tested with input voltage <inline-formula> <tex-math notation="LaTeX">V_{\mathrm {IN}} </tex-math></inline-formula> ranging from 12 to 48 V, delivering up to 4 W of power at 1-V <inline-formula> <tex-math notation="LaTeX">V_{\mathrm {O}} </tex-math></inline-formula>. It achieves peak efficiency of 90.7% and 85.6% for 12-V/1-V and 48-V/1-V power conversion, respectively, at an effective switching frequency of 4.5 MHz, which is based on a three-phase operation with each phase at 1.5 MHz. The adaptive <inline-formula> <tex-math notation="LaTeX">V_{\mathrm {CF}} </tex-math></inline-formula> rebalancing technique reduces <inline-formula> <tex-math notation="LaTeX">V_{\mathrm {CF}} </tex-math></inline-formula> imbalance error by up to 65.1%. Overall, the proposed 3P4S hybrid switching power converter offers an efficient and robust solution for direct dc-dc conversion with a wide <inline-formula> <tex-math notation="LaTeX">V_{\mathrm {IN}} </tex-math></inline-formula> range.
MR fingerprinting allows rapid simultaneous quantification of T1 and T2 relaxation times. This study assessed the utility of MR fingerprinting in differentiating common types of adult intra-axial ...brain tumors.
MR fingerprinting acquisition was performed in 31 patients with untreated intra-axial brain tumors: 17 glioblastomas, 6 World Health Organization grade II lower grade gliomas, and 8 metastases. T1, T2 of the solid tumor, immediate peritumoral white matter, and contralateral white matter were summarized within each ROI. Statistical comparisons on mean, SD, skewness, and kurtosis were performed by using the univariate Wilcoxon rank sum test across various tumor types. Bonferroni correction was used to correct for multiple-comparison testing. Multivariable logistic regression analysis was performed for discrimination between glioblastomas and metastases, and area under the receiver operator curve was calculated.
Mean T2 values could differentiate solid tumor regions of lower grade gliomas from metastases (mean, 172 ± 53 ms, and 105 ± 27 ms, respectively;
= .004, significant after Bonferroni correction). The mean T1 of peritumoral white matter surrounding lower grade gliomas differed from peritumoral white matter around glioblastomas (mean, 1066 ± 218 ms, and 1578 ± 331 ms, respectively;
= .004, significant after Bonferroni correction). Logistic regression analysis revealed that the mean T2 of solid tumor offered the best separation between glioblastomas and metastases with an area under the curve of 0.86 (95% CI, 0.69-1.00;
< .0001).
MR fingerprinting allows rapid simultaneous T1 and T2 measurement in brain tumors and surrounding tissues. MR fingerprinting-based relaxometry can identify quantitative differences between solid tumor regions of lower grade gliomas and metastases and between peritumoral regions of glioblastomas and lower grade gliomas.
•A new microchannel with triangular cavities and rectangular ribs is presented.•The combined effects of cavities and ribs are studied.•The heat transfer mechanism of microchannel is analyzed by ...entropy generation.•The geometric parameters of the new microchannel are discussed.•The new microchannel yields the best overall performance with η=1.619 at Re=500.
A novel microchannel heat sink with triangular cavities and rectangular ribs (TC–RR) is presented and the characteristics of fluid flow and heat transfer are studied numerically for Reynolds number (Re) ranging from 173 to 635. The effects of cavities and ribs on the Nusselt number and friction factor are investigated. The method of entropy generation minimization is also adopted to analysis the thermal performance of the micro heat sink and the mechanism of heat transfer enhancement. The overall performance of the new micro heat sink is assessed based on thermal enhancement factor and augmentation entropy generation number. The results show that the TC–RR microchannel obtains significant heat transfer enhancement attributed to the interruption and redevelopment of thermal boundary layer, the intensified mainstream disturbance and the chaotic mixing between the cold and hot water. In addition, the influence of relative rib width (α) and relative cavity width (β) on the flow and heat transfer performance is investigated. The thermal enhancement factor for TC–RR microchannel with α=0.3 and β=2.24 achieves 1.619 at Re=500. Due to more uniform temperature of bottom surface, less irreversibility and better heat transfer performance, the novel micro heat sink is more promising for microelectronic cooling system.
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