Mesoscale Simulation of Polymer Pyrolysis by Coarse-Grained Molecular Dynamics: A Parametric Study.

Full comprehension of the pyrolysis of polymer materials is crucial for the design and application of thermal protection systems; however, it involves complex phenomena at different spatial and temporal scales. To bridge the gap between the abundant atomistic simulations and continuum modeling in the literature, we perform a novel mesoscale study of the pyrolysis process using coarse-grained molecular dynamics (CG MD) simulations. Polyethylene (PE) consisting of united atoms including implicit hydrogen is considered a model polymer, and the configurational change of PE in thermal degradation is modeled by applying the bond-breaking phenomenon based on bond energy or bond length criteria. A cook-off simulation is implemented to optimize the heuristic protocol of bond dissociation by comparing the reaction products with a ReaxFF simulation. The aerobic hyperthermal pyrolysis under oxygen bombardment is simulated at a large scale of hundreds of nanometers to observe the intricate phenomena occurring from the surface to the depth inside the material. The intrinsic thermal durability of the model polymer at extreme conditions with and without oxygen environment can be effectively simulated from the proposed mesoscale simulation to predict important thermal degradation properties required for continuum-scale pyrolysis and ablation simulations. This work serves as an initial investigation of polymer pyrolysis at the mesoscale and helps understand the concept at a larger scale.

Comparison of epidural, spinal, and saddle block for holmium laser enucleation of prostate (HoLEP): A prospective randomized, comparative study.

BACKGROUND: Holmium laser enucleation of the prostate (HoLEP) has become an important treatment modality for benign prostate hypertrophy. The aim of the present study was to compare regional anesthesia methods for HoLEP operation and to determine the optimal technique. METHODS: Sixty patients with American Society of Anesthesiologists scores of I-III were randomly allocated into 3 groups. Patients in group E received an epidural block with 75 mg of bupivacaine plus 50 µg of fentanyl. In group S, 15 mg of bupivacaine and 50 µg fentanyl were used for spinal anesthesia. In group SA, patients received saddle block with 15 mg of bupivacaine and 50 µg of fentanyl. RESULTS: Time to T10 dermatome block and to maximal level block were longest in group E (P < .05), and maximal sensorial block level was higher in group E than group SA (P < .05). There was a significant difference in postoperative motor block, but no difference in systolic blood pressure and heart rate. CONCLUSION: Among 3 techniques, saddle block might be preferable in HoLEP because an adequate sensorial level was achieved with lower motor block and stable hemodynamics.

Role of erector spinae plane block in controlling functional abdominal pain: Case reports.

RATIONALE: Functional abdominal pain is an intractable medical condition that often reduces quality of life. Celiac plexus block is a representative intervention for managing intractable abdominal pain. However, celiac plexus block can be technically difficult to perform and carries the risk of potential complications. During erector spinae plane block (ESPB), the injectate can enter the paravertebral space and reach the sympathetic chain. If local anesthetics spread to the sympathetic chain that supplies fibers to the splanchnic nerve, abdominal pain theoretically could be reduced. PATIENT CONCERNS: Three patients suffered from abdominal pain of unknown cause, and no medical abnormalities were found in various examinations. DIAGNOSIS: As a result of collaboration with related medical departments, the abdominal symptoms of the patients were suspected to be functional abdominal pain. INTERVENTIONS: We successfully controlled symptoms by performing ESPB at the lower thoracic level in 3 patients with functional abdominal pain. OUTCOMES: After the procedure, the patients' abdominal pain improved significantly over several months. LESSONS: We suggest that lower thoracic ESPB could be an option for management of functional abdominal pain.

The small molecule kobusone can stimulate islet ß-cell replication in vivo.

OBJECTIVE: To investigate the ability of kobusone to reduce high glucose levels and promote ß-cell proliferation. METHODS: Four-week-old female db/db mice were assigned to the kobusone (25 mg/kg body weight, intraperitoneally twice a day) or control group (same volume of PBS). Glucose levels and body weight were measured twice a week. After 6 weeks, intraperitoneal glucose tolerance tests and immunohistochemical studies were performed, and insulin levels were determined. The expression of mRNAs involved in cell proliferation, such as PI3K, Akt, cyclin D3 and p57Kip2, was measured by quantitative reverse transcription polymerase chain reaction (RT-qPCR). RESULTS: Kobusone reduced blood glucose levels after 3 weeks and more strongly increased serum insulin levels than the vehicle. Immunohistochemistry illustrated that kobusone increased 5-bromo-2'-deoxyuridine incorporation into islet ß-cells, suggesting that it can stimulate islet ß-cell replication in vivo. RT-qPCR indicated that kobusone upregulated the mRNA expression of PI3K, Akt, and cyclin D3 and downregulated that of p57Kip2. CONCLUSION: Our findings suggest that kobusone is a potent pancreatic islet ß-cell inducer that has the potential to be developed as an anti-diabetic agent.

Midazolam anaphylaxis during general anesthesia: A case report.

RATIONALE: Midazolam is known as a safe drug and is widely used as a sedative and an anesthetic adjuvant. Therefore, there is a lack of awareness that midazolam can cause anaphylaxis. Midazolam anaphylaxis is rare, and only a few cases have been reported, but such a risk is always present. In this study, we report a case of midazolam anaphylaxis by an intravenous injection, in the prone position, during general anesthesia. PATIENT CONCERNS: A 62-year-old woman was intravenously administered 1 mg midazolam during general anesthesia, and sudden severe hypotension, bronchospasm, decreased oxygen saturation, erythema, and diarrhea occurred. DIAGNOSIS: Midazolam anaphylaxis was presumptively diagnosed by clinical symptoms and was confirmed by an intradermal test after 9 weeks. INTERVENTIONS: The patient was treated with 100% oxygen, large volume of fluid, epinephrine, phenylephrine, ephedrine, dexamethasone and prednisolone, ranitidine, and flumazenil. OUTCOMES: Severe hypotension and decreased oxygen saturation were resolved within 20 minutes of the onset of anaphylaxis, and the patient was discharged after 3 days without any sequelae. LESSONS: Midazolam anaphylaxis is very rare, but it can happen always. Therefore, the possibility of anaphylaxis due to midazolam should be considered and always be prepared for treatment.

Audio-Tactile Skinny Buttons for Touch User Interfaces.

This study proposes a novel skinny button with multimodal audio and haptic feedback to enhance the touch user interface of electronic devices. The active material in the film-type actuator is relaxor ferroelectric polymer (RFP) poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] blended with poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], which produces mechanical vibrations via the fretting vibration phenomenon. Normal pressure applied by a human fingertip on the film-type skinny button mechanically activates the locally concentrated electric field under the contact area, thereby producing a large electrostrictive strain in the blended RFP film. Multimodal audio and haptic feedback is obtained by simultaneously applying various electric signals to the pairs of ribbon-shaped top and bottom electrodes. The fretting vibration provides tactile feedback at frequencies of 50-300 Hz and audible sounds at higher frequencies of 500 Hz to 1 kHz through a simple on-off mechanism. The advantage of the proposed audio-tactile skinny button is that it restores the "click" sensation to the popular virtual touch buttons employed in contemporary electronic devices.

Localized Fretting-Vibrotactile Sensations for Large-Area Displays.

Tactile perception in large-area displays is currently attracting substantial research attention since, in conjunction with visible and auditory sensations, it provides more immersive and realistic interactions with displayed contents. Here, a new vibrotactile display based on the fretting phenomenon is developed for the first time to provide localized tactile feedback on a large-area display. Normal pressure by a human fingertip activates a locally concentrated electric field in a relaxor ferroelectric polymer (RFP) film under the contact area, which produces a localized electrostrictive strain. The synergistic interplay among the localized electric field, electrostrictive deformation of the RFP film, and contact area dramatically amplifies acoustic vibrations near the contact edge of a human fingertip. A blend of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer and poly(vinylidene fluoride-trifluoroethylene) (55:45) copolymer is proposed for the RFP to provide an enhanced actuation performance even at elevated temperatures. The fretting-vibrotactile mechanism has several interesting properties, such as tactile feedback on a stationary fingertip, pressure-responsive simple on-off mechanism, multitouch interaction, excellent transparency, and easy integration with capacitive or resistive touch sensors and friction-based haptic-feedback mechanisms. An array of RFP film vibrators can provide addressable content-related multiple tactile feedback on large-area displays by modulating the frequency, amplitude, and profile of the driving voltage signals.

Tribological Behavior of Grafted Nanoparticle on Polymer-Brushed Walls: A Dissipative Particle Dynamics Study.

Two contacting surfaces grafted with polymer brushes have potential applications due to their extraordinary lubricating behavior. However, the polymer brushes may have poor mechanical stability under high normal and shear stresses, which is a challenge for practical usage of polymer brush systems. In this study, we propose the use of grafted nanoparticles as nanobearings on polymer-brush-coated surfaces to alleviate the harsh working conditions of polymer brushes and to improve their mechanical stability. We have performed dissipative particle dynamics (DPD) simulations to investigate the tribological interaction between grafted nanoparticle and parallel walls with noncharged polymer brushes in the presence of explicit solvent. The influences of several parameters (solvent quality, brush miscibility, etc.) on the tribological behavior of the system are investigated. The grafted nanoparticle obviously acts as a nanobearing that partially replaces the sliding contact between two brushed walls with rolling contact between the grafted nanoparticle and two brushed walls and reduces the number of DPD particles withstanding high force. Although the introduction of the grafted nanoparticle into polymer-brushed walls increases the friction coefficient by 20-30%, it does not greatly decrease lubrication of the brushed walls, while still helping in stabilizing the system of polymer brushes to be used with liquids with low viscosity, such as water. The DPD simulation results and analysis performed in this study would be beneficial in designing systems with polymer-brushed surfaces and grafted nanoparticles.

Hand-Driven Gyroscopic Hybrid Nanogenerator for Recharging Portable Devices.

With the rise of portable and wearable electronics, a fast-charging, long-lasting power solution is needed; thus, there are attempts to harvest energy from the ambient environment. Mechanical energy harvesting through piezoelectric and triboelectric nanogenerators (PENG and TENG) is a promising approach due to their light weight, low cost, and high-power density in comparison to other technologies. Both types of generators are capable of charging portable and smart devices on their own by converting mechanical energy into electricity. However, most previous methods have excessive input conditions, such as high rpm and input frequency, that can be only applied with other actuators. Here, a hand-held gyroscopic generator is presented that uses the gyroscopic principle to reach a rotation rate above 8000 rpm with only hand input. The generator comprises a rotating flywheel inside a casing. Both the flywheel and casing have a TENG, and with a hybrid generator, electrical power is produced from rotation, vibration, and centrifugal force during operation. The device shows a consistent open-circuit voltage (V OC) of 90 V and a closed-circuit current (I CC) of 11 µA with a frequency of 200 Hz. As a stand-alone device, this generator can power portable sensors and smartphones through hand rotation.

Laser-Induced Particle Adsorption on Atomically Thin MoS2.

Atomically thin molybdenum disulfide (MoS2) shows great potential for use in nanodevices because of its remarkable electronic, optoelectronic, and mechanical properties. These material properties are often dependent on the thickness or the number of layers, and hence Raman spectroscopy is widely used to characterize the thickness of atomically thin MoS2 due to the sensitivity of the vibrational spectrum to thickness. However, the lasers used in Raman spectroscopy can increase the local surface temperature and eventually damage the upper layers of the MoS2, thereby changing the aforementioned material properties. In this work, the effects of lasers on the topography and material properties of atomically thin MoS2 were systematically investigated using Raman spectroscopy and atomic force microscopy. In detail, friction force microscopy was used to study the friction characteristics of atomically thin MoS2 as a function of laser powers from 0.5 to 20 mW and number of layers from 1 to 3. It was found that particles formed on the top surface of the atomically thin MoS2 due to laser-induced thermal effects. The degree of particle formation increased as the laser power increased, prior to the thinning of the atomically thin MoS2. In addition, the degree of particle formation increased as the number of MoS2 layers increased, which suggests that the thermal behavior of the supported MoS2 may differ depending on the number of layers. The particles likely originated from the atmosphere due to laser-induced heating, but could be eliminated via appropriate laser powers and exposure times, which were determined experimentally. The outcomes of this work indicate that thermal management is crucial in the design of reliable nanoscale devices based on atomically thin MoS2.

Opto-mechanical analysis of nonlinear elastomer membrane deformation under hydraulic pressure for variable-focus liquid-filled microlenses.

Nonlinear large deformation of a transparent elastomer membrane under hydraulic pressure was analyzed to investigate its optical performance for a variable-focus liquid-filled membrane microlens. In most membrane microlenses, actuators control the hydraulic pressure of optical fluid so that the elastomer membrane together with the internal optical fluid changes its shape, which alters the light path of the microlens to adapt its optical power. A fluid-structure interaction simulation was performed to estimate the transient behavior of the microlens under the operation of electroactive polymer actuators, demonstrating that the viscosity of the optical fluid successfully stabilizes the fluctuations within a fairly short period of time during dynamic operations. Axisymmetric nonlinear plate theory was used to calculate the deformation profile of the membrane under hydrostatic pressure, with which optical characteristics of the membrane microlens were estimated. The effects of gravitation and viscoelastic behavior of the elastomer membrane on the optical performance of the membrane microlens were also evaluated with finite element analysis.

Melanogenesis effect of Cordyceps militaris culture broth on the melanin formation of B16F0 melanoma cells.

The effect of Cordyceps militaris culture broth (CMB) on melanogenesis in B16F0 melanoma cells was evaluated by measurement of the melanin concentration after 3 days of incubation. The B16F0 melanoma cells were treated with various concentrations of CMB 10-100 µg/mL and arbutin of 200 µM. Phenolic content and antioxidant activity of CMB were also measured. Phenolic content of CMB was 3.28 mg/g. The DPPH radical scavenging and ferric ion donating activities were 79.64% and 0.16, respectively. The melanin concentration and cell viability of melanoma cells by arbutin treatment decreased to 43% and 91% of the control, respectively. The CMB treatment showed a significant inhibitory effect of melanin production by 29%, 50%, and 56% at 50, 80, and 100 µg/mL concentration treatment, respectively, while over 90% of cells were viable. The CMB treatment at 50, 80, and 100 µg/mL concentrations in cultivation decreased extracellular melanin release induced by 3-isobutyl-1-methylxanthine (IBMX) treatment by 19%, 38%, and 48%, respectively. The CMB showed inhibitory activity against intracellular tyrosinase extracted from melanoma cells, while it had no inhibition on the activity of mushroom tyrosinase. The cellular glutathione contents were enhanced by CMB treatment in a concentration-dependent manner. These results suggested that CMB suppressed cellular tyrosinase activity and total melanin content in cultured B16F0 melanoma cells without any significant effects on cell proliferation and it might be candidate anti-melanogenic agent.

Varifocal liquid-filled microlens operated by an electroactive polymer actuator.

We designed, fabricated, and characterized varifocal microlenses, whose focal length varies along with the deformation of a transparent elastomer membrane under hydraulic pressure tailored by electroactive polymer actuators. The microfluidic channel of the microlens was designed to be embedded between silicon and glass so that transient fluctuation of the optical fluid and elastomer membrane is effectively suppressed, and thus the microlens is optically stabilized in a reduced time. Multilayered poly(vinylidene fluoride-trifluoroethylene-clorotrifluoroethylene) actuators were also developed and integrated onto the microfluidic chambers. We demonstrated that the developed microlenses are suitable for use in microimaging systems to make their foci tunable.