Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 45
Filtrar
Mais filtros

Base de dados
País/Região como assunto
Tipo de documento
Intervalo de ano de publicação
1.
Nature ; 614(7946): 81-87, 2023 02.
Artigo em Inglês | MEDLINE | ID: mdl-36725999

RESUMO

Micro-LEDs (µLEDs) have been explored for augmented and virtual reality display applications that require extremely high pixels per inch and luminance1,2. However, conventional manufacturing processes based on the lateral assembly of red, green and blue (RGB) µLEDs have limitations in enhancing pixel density3-6. Recent demonstrations of vertical µLED displays have attempted to address this issue by stacking freestanding RGB LED membranes and fabricating top-down7-14, but minimization of the lateral dimensions of stacked µLEDs has been difficult. Here we report full-colour, vertically stacked µLEDs that achieve, to our knowledge, the highest array density (5,100 pixels per inch) and the smallest size (4 µm) reported to date. This is enabled by a two-dimensional materials-based layer transfer technique15-18 that allows the growth of RGB LEDs of near-submicron thickness on two-dimensional material-coated substrates via remote or van der Waals epitaxy, mechanical release and stacking of LEDs, followed by top-down fabrication. The smallest-ever stack height of around 9 µm is the key enabler for record high µLED array density. We also demonstrate vertical integration of blue µLEDs with silicon membrane transistors for active matrix operation. These results establish routes to creating full-colour µLED displays for augmented and virtual reality, while also offering a generalizable platform for broader classes of three-dimensional integrated devices.

2.
Nat Mater ; 22(12): 1470-1477, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-38012388

RESUMO

Three-dimensional (3D) hetero-integration technology is poised to revolutionize the field of electronics by stacking functional layers vertically, thereby creating novel 3D circuity architectures with high integration density and unparalleled multifunctionality. However, the conventional 3D integration technique involves complex wafer processing and intricate interlayer wiring. Here we demonstrate monolithic 3D integration of two-dimensional, material-based artificial intelligence (AI)-processing hardware with ultimate integrability and multifunctionality. A total of six layers of transistor and memristor arrays were vertically integrated into a 3D nanosystem to perform AI tasks, by peeling and stacking of AI processing layers made from bottom-up synthesized two-dimensional materials. This fully monolithic-3D-integrated AI system substantially reduces processing time, voltage drops, latency and footprint due to its densely packed AI processing layers with dense interlayer connectivity. The successful demonstration of this monolithic-3D-integrated AI system will not only provide a material-level solution for hetero-integration of electronics, but also pave the way for unprecedented multifunctional computing hardware with ultimate parallelism.

3.
Angew Chem Int Ed Engl ; 62(4): e202212942, 2023 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-36413636

RESUMO

The LiOH-based cathode chemistry has demonstrated potential for high-energy Li-O2 batteries. However, the understanding of such complex chemistry remains incomplete. Herein, we use the combined experimental methods with ab initio calculations to study LiOH chemistry. We provide a unified reaction mechanism for LiOH formation during discharge via net 4 e- oxygen reduction, in which Li2 O2 acts as intermediate in low water-content electrolyte but LiHO2 as intermediate in high water-content electrolyte. Besides, LiOH decomposes via 1 e- oxidation during charge, generating surface-reactive hydroxyl species that degrade organic electrolytes and generate protons. These protons lead to early removal of LiOH, followed by a new high-potential charge plateau (1 e- water oxidation). At following cycles, these accumulated protons lead to a new high-potential discharge plateau, corresponding to water formation. Our findings shed light on understanding of 4 e- cathode chemistries in metal-air batteries.

4.
Nano Lett ; 21(18): 7579-7586, 2021 09 22.
Artigo em Inglês | MEDLINE | ID: mdl-34469158

RESUMO

Na-ion and K-ion batteries are promising alternatives for large-scale energy storage due to their abundance and low cost. Intercalation of these large ions could cause irreversible structural deformation and partial to complete amorphization in the crystalline electrodes. A lack of understanding of the dynamic changes in the amorphous nanostructure during battery operation is the bottleneck for further developments. Here, we report the utilization of in-operando digital image correlation and XRD techniques to probe dynamic changes in the amorphous phase of iron phosphate during potassium ion intercalation. In-operando XRD demonstrates amorphization in the electrode's nanostructure during the first charge and discharge cycle. Additionally, ex situ HR-TEM further confirms the amorphization after potassium-ion intercalation. An in situ strain analysis detects reversible deformations associated with redox reactions in the amorphous phases. Our approach offers new insights into the mechanism of ion intercalation in the amorphous nanostructure which are highly potent for the development of next-generation batteries.


Assuntos
Fosfatos , Potássio , Eletrodos , Íons , Ferro
5.
J Med Internet Res ; 23(2): e26257, 2021 02 22.
Artigo em Inglês | MEDLINE | ID: mdl-33539312

RESUMO

BACKGROUND: As the COVID-19 pandemic continues, an initial risk-adapted allocation is crucial for managing medical resources and providing intensive care. OBJECTIVE: In this study, we aimed to identify factors that predict the overall survival rate for COVID-19 cases and develop a COVID-19 prognosis score (COPS) system based on these factors. In addition, disease severity and the length of hospital stay for patients with COVID-19 were analyzed. METHODS: We retrospectively analyzed a nationwide cohort of laboratory-confirmed COVID-19 cases between January and April 2020 in Korea. The cohort was split randomly into a development cohort and a validation cohort with a 2:1 ratio. In the development cohort (n=3729), we tried to identify factors associated with overall survival and develop a scoring system to predict the overall survival rate by using parameters identified by the Cox proportional hazard regression model with bootstrapping methods. In the validation cohort (n=1865), we evaluated the prediction accuracy using the area under the receiver operating characteristic curve. The score of each variable in the COPS system was rounded off following the log-scaled conversion of the adjusted hazard ratio. RESULTS: Among the 5594 patients included in this analysis, 234 (4.2%) died after receiving a COVID-19 diagnosis. In the development cohort, six parameters were significantly related to poor overall survival: older age, dementia, chronic renal failure, dyspnea, mental disturbance, and absolute lymphocyte count <1000/mm3. The following risk groups were formed: low-risk (score 0-2), intermediate-risk (score 3), high-risk (score 4), and very high-risk (score 5-7) groups. The COPS system yielded an area under the curve value of 0.918 for predicting the 14-day survival rate and 0.896 for predicting the 28-day survival rate in the validation cohort. Using the COPS system, 28-day survival rates were discriminatively estimated at 99.8%, 95.4%, 82.3%, and 55.1% in the low-risk, intermediate-risk, high-risk, and very high-risk groups, respectively, of the total cohort (P<.001). The length of hospital stay and disease severity were directly associated with overall survival (P<.001), and the hospital stay duration was significantly longer among survivors (mean 26.1, SD 10.7 days) than among nonsurvivors (mean 15.6, SD 13.3 days). CONCLUSIONS: The newly developed predictive COPS system may assist in making risk-adapted decisions for the allocation of medical resources, including intensive care, during the COVID-19 pandemic.


Assuntos
COVID-19/diagnóstico , COVID-19/mortalidade , Fatores Etários , Idoso , Cuidados Críticos/estatística & dados numéricos , Demência/epidemiologia , Feminino , Humanos , Falência Renal Crônica/epidemiologia , Tempo de Internação/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Pandemias , Prognóstico , Modelos de Riscos Proporcionais , Curva ROC , República da Coreia/epidemiologia , Estudos Retrospectivos , Fatores de Risco , Índice de Gravidade de Doença , Taxa de Sobrevida
6.
Phys Chem Chem Phys ; 22(14): 7537-7545, 2020 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-32219231

RESUMO

Understanding how electrons and protons move in a coupled manner and affect one another is important to the design of proton-electron conductors and achieving biological transport in synthetic materials. In this study, a new methodology is proposed that allows for the quantification of the degree of coupling between electrons and protons in tyrosine-rich peptides and metal oxide hybrid films at room temperature under a voltage bias. This approach is developed according to the Onsager principle, which has been thoroughly established for the investigation of mixed ion-electron conductors with electron and oxide ion vacancies as carriers at high temperatures. Herein, a new device platform using electron-blocking electrodes provides a new strategy to investigate the coupling of protons and electrons in bulk materials beyond the molecular level investigation of coupled proton and electron transfer. Two Onsager transport parameters, αi* and σe', are obtained from the device, and the results of these transport parameters demonstrate that the coupled transport of electrons and protons inside the hybrid film plays an important role in the macroscopic-scale conduction. The results suggest that an average of one electron is dragged by one proton in the absence of a direct driving force for electron movement ∇ηe.


Assuntos
Técnicas de Química Analítica/instrumentação , Transporte de Elétrons/fisiologia , Elétrons , Compostos de Manganês/química , Óxidos/química , Peptídeos/química , Prótons , Transporte Biológico/fisiologia
7.
J Clin Densitom ; 23(1): 82-91, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-30120026

RESUMO

INTRODUCTION: The aims of this study were to (1) assess the bone mineral density (BMD) around the knee joint, (2) determine the correlation between central and knee BMDs, and (3) investigate the factors associated with BMD around the knee joint in patients with knee osteoarthritis (OA). METHODOLOGY: This cross-sectional study included 122 patients who underwent total knee arthroplasty. Central and knee dual-energy X-ray absorptiometry was performed preoperatively. BMD at 6 regions of interest (ROIs) around the knee joint were measured, and their correlations with central BMD were determined using Spearman's correlation analysis. Lower limb alignment, severity of OA, body mass index (BMI), preoperative functional and pain scores were assessed to elucidate the factors associated with knee BMD using linear regression analysis. RESULTS: Around the knee joint, BMD was the lowest at the distal femoral metaphysis and lateral tibial condyle. Knee BMD was significantly correlated with central BMD. However, the correlation coefficients varied by the ROI. Additionally, multivariate analysis revealed different associations with respect to the regions around the knee joint. Varus alignment of the lower limb was associated with increased BMD of the medial condyles and decreased BMD of lateral condyles. High grade OA was a protective factor; it was associated with increased BMD at the lateral condyles of the femur and tibia. Higher BMI was an independent protective factor in all ROIs around the knee joint except the lateral femoral condyles. Lower functional level was not associated with decreased BMD, whereas a higher pain score was significantly associated with lower BMD at the proximal tibial metaphysis. CONCLUSIONS: Knee BMD was significantly correlated with central BMD. However, the correlations varied with the regions around the knee joint probably due to their independent association with the alignment of the lower limb, severity of OA, BMI, and preoperative pain level.


Assuntos
Densidade Óssea , Articulação do Joelho/anatomia & histologia , Absorciometria de Fóton , Idoso , Idoso de 80 Anos ou mais , Artroplastia do Joelho , Índice de Massa Corporal , Estudos Transversais , Feminino , Fêmur/anatomia & histologia , Fêmur/patologia , Humanos , Modelos Lineares , Masculino , Pessoa de Meia-Idade , Osteoartrite do Joelho/patologia , Osteoartrite do Joelho/cirurgia , Índice de Gravidade de Doença , Tíbia/anatomia & histologia , Tíbia/patologia
8.
Eur J Orthop Surg Traumatol ; 29(1): 227-230, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29915953

RESUMO

BACKGROUND: A two-stage approach to total knee arthroplasty (TKA) using an antibiotic-impregnated articulating cement spacer is an option for an infected arthritic knee. Vancomycin combined with broad-spectrum antibiotics can be used to make an antibiotic-impregnated articulating cement spacer. Causative organisms are sometimes not confirmed before surgery. Joint infections of multidrug-resistant organisms are increasing. Therefore, routine combinations of antibiotics may not be effective. METHODS AND RESULTS: We present a case of a patient who developed vancomycin-resistant Pseudomonas aeruginosa infection in an arthritic knee. A 71-year-old man was initially diagnosed with pyogenic arthritis caused by Staphylococcus aureus. He underwent arthroscopic debridement elsewhere. However, the infection persisted. He was referred to our hospital, and we performed a two-stage TKA using a vancomycin-based antibiotic-impregnated articulating cement spacer. Vancomycin-resistant P. aeruginosa was identified after surgery. Intravenous colistin was added. However, this failed, either because vancomycin was not effective against P. aeruginosa, or because insufficient systemic colistin due to colistin-induced acute kidney injury. Therefore, debridement was repeated, and colistin-loaded cement spacer was inserted. The spacer delivered high concentrations of colistin to the infected joint with decreased systemic effects. Thus, less systemic colistin was used. The infection was controlled without recurrent acute kidney injury. One year after surgery, conversion to TKA was successfully performed. CONCLUSION: A two-stage approach to TKA using a colistin-loaded articulating cement spacer can be used for an arthritic knee infected by vancomycin-resistant P. aeruginosa. Furthermore, local administration of colistin using a cement spacer can reduce the systemic side effects of colistin.


Assuntos
Antibacterianos/administração & dosagem , Artrite Infecciosa/cirurgia , Artroplastia do Joelho/métodos , Colistina/administração & dosagem , Infecções por Pseudomonas/tratamento farmacológico , Pseudomonas aeruginosa/efeitos dos fármacos , Idoso , Artrite Infecciosa/microbiologia , Artroplastia do Joelho/efeitos adversos , Artroplastia do Joelho/instrumentação , Cimentos Ósseos , Desbridamento , Humanos , Masculino , Infecções por Pseudomonas/microbiologia , Reoperação , Infecções Estafilocócicas/complicações , Resistência a Vancomicina
9.
Opt Lett ; 43(19): 4590-4593, 2018 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-30272690

RESUMO

Crumple-structured two-dimensional MoS2 was evaluated as an essential element for future optoelectronic and stretchable devices owing to its interesting optical properties. This Letter reports the characteristics of the crumpled structure of MoS2 directly layered on a MoS2 sheet by chemical vapor deposition. The crumpling structure is presented as a method for selectively layering MoS2 with crumpled layered patterning and tunable optical properties as a crumpled structure on a single substrate. Optical analysis by the fast Fourier transform revealed the distribution characteristics of the crumple structure, and a Raman, photoluminescence, and optical absorption analysis confirmed the change in peak shift and intensity according to the degree of the crumpled structure. This material has potential future optoelectronic applications.

10.
Scand J Med Sci Sports ; 28(12): 2604-2610, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30102809

RESUMO

BACKGROUND: Some patients with recurrent symptomatic instability after primary anterior cruciate ligament (ACL) reconstruction have an extension deficiency (ED). This study (a) compared preoperative clinical conditions between the ED and non-ED groups undergoing revision ACL reconstruction, (b) documented clinical and arthroscopic findings in ACL-reconstructed patients with reinstability and ED, and (c) determined whether the ED could be resolved and whether the clinical results of revision surgery differed between the ED and non-ED groups. METHODS: This study included 58 patients who underwent revision ACL reconstruction. Patients were divided into the ED and non-ED groups. Preoperatively, the demographics and clinical conditions of the two groups were compared. Intraoperatively, the pathological structures that related to ED were documented. After surgery, the degree of postoperative ED and functional outcomes were compared between the two groups at 2-year follow-up. RESULTS: The International Knee Documentation Committee subjective score and SF-36 physical component summary scores were worse in the ED group than the non-ED group preoperatively (54 vs 48 [P = 0.014]; 42 vs 39 [P = 0.031], respectively). Intraoperatively, the ED group showed significantly more frequent graft malposition (50% vs 5%), anvil osteophytes (44% vs 0%), and scarring around posterior intercondylar notch (100% vs 0%). However, there was no difference in the degree of postoperative ED and functional outcome between the two groups at follow-up. CONCLUSIONS: ED in patients with recurrent instability after primary ACL reconstruction could be treated with good clinical result by addressing the pathological conditions causing ED in addition to ACL re-reconstruction.


Assuntos
Reconstrução do Ligamento Cruzado Anterior , Ligamento Cruzado Anterior/cirurgia , Cartilagem Articular/patologia , Articulação do Joelho/fisiopatologia , Reoperação , Adolescente , Adulto , Feminino , Humanos , Instabilidade Articular/fisiopatologia , Masculino , Pessoa de Meia-Idade , Amplitude de Movimento Articular , Resultado do Tratamento , Adulto Jovem
11.
BMC Musculoskelet Disord ; 19(1): 274, 2018 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-30064411

RESUMO

BACKGROUND: We sought to document the incidences of deep vein thrombosis (DVT) before and after total knee arthroplasty (TKA). In addition, we aimed to explor whether routine preoperative DVT evaluation was useful to establish DVT treatment strategies after TKA. Finally, we wanted to evaluate whether the incidences of DVT differed between patients undergoing unilateral and staged bilateral TKA within the same hospitalization period. METHODS: The retrospective study included 153 consecutive patients (253 knees) with osteoarthritis who underwent primary TKA. After surgery, mechanical compression devices (only) were used for DVT prophylaxis. DVT status before and after TKA was determined via 128-row, multidetector, computed tomography/indirect venography. RESULTS: Overall, the preoperative DVT incidence was 2.6% per patient and 1.6% per knee. All preoperative DVTs were distal in nature and asymptomatic. After TKA, newly developed thrombi were evident in various calf veins, without propagation of any pre-existing thrombi. Postoperatively, the overall incidences of DVT were 69.9% per patient and 58.5% per knee. The DVT incidences were 66% per patient and 69.8% per knee in the unilateral TKA group. In contrast, the incidences were 72% per patient and 55.5% per knee in the staged bilateral TKA group. There was one case of symptomatic distal (unilateral TKA; 0.65% per patient and 0.4% per knee) and proximal DVT (bilateral TKA; 0.65% per patient and 0.4% per knee), respectively. CONCLUSIONS: The incidence of symptomatic DVT was low in Asian patients treated with mechanical compression devices alone, although substantial portion of patients had DVT after surgery. Routine preoperative DVT evaluation is probably not necessary; preoperative DVT was rare and of limited clinical relevance. Furthermore, staged bilateral TKA during a single period of hospitalization does not increase the incidence of DVT.


Assuntos
Artroplastia do Joelho/efeitos adversos , Angiografia por Tomografia Computadorizada/métodos , Tomografia Computadorizada Multidetectores/métodos , Flebografia/métodos , Trombose Venosa/diagnóstico por imagem , Trombose Venosa/epidemiologia , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Incidência , Masculino , Pessoa de Meia-Idade , Valor Preditivo dos Testes , Estudos Retrospectivos , Seul/epidemiologia , Resultado do Tratamento , Trombose Venosa/prevenção & controle
12.
J Arthroplasty ; 33(9): 2835-2842, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-29773278

RESUMO

BACKGROUND: Recently, concerns arose over the medial tibial bone resorption of a novel cobalt-chromium implant. This study aimed at investigating the effects of tibial component material, design, and patient factors on periprosthetic bone resorption and at determining its association with clinical outcomes after total knee arthroplasty (TKA). METHODS: A total of 462 primary TKAs using 5 types of implants were included. To evaluate tibial periprosthetic bone resorption, we assessed radiolucent lines and change in bone mineral density at the medial tibial condyle (BMDMT). Factors related to bone resorption were assessed using regression analysis. Clinical outcomes were also evaluated with respect to periprosthetic bone resorption. RESULTS: Compared to titanium implants, cobalt-chromium implants showed a higher incidence of complete radiolucent lines (23.1% vs 7.9% at 2 years post-TKA) and a greater degree of BMDMT reduction. However, there was no significant difference between the implants made of the same material. Increased medial tibial bone resorption was associated with male sex, osteoporosis, larger preoperative varus deformity, longer follow-up period, and lower body mass index. The periprosthetic bone resorption was not associated with clinical outcomes including changes in range of motion and Western Ontario and McMaster Universities Osteoarthritis Index score. Furthermore, no cases warranted additional surgery. CONCLUSION: Periprosthetic bone resorption was associated with implant material but not with implant design. Moreover, patient factors were related to the medial tibial bone resorption post-TKA. However, the periprosthetic bone resorption was not associated with short-term clinical outcomes. We contend that researchers should incorporate integrative considerations when developing and assessing novel implants.


Assuntos
Artroplastia do Joelho , Reabsorção Óssea , Cromo/efeitos adversos , Cobalto/efeitos adversos , Prótese do Joelho , Titânio/efeitos adversos , Idoso , Idoso de 80 Anos ou mais , Índice de Massa Corporal , Densidade Óssea , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Desenho de Prótese , Amplitude de Movimento Articular , Estudos Retrospectivos , Índice de Gravidade de Doença , Tíbia/cirurgia , Resultado do Tratamento
13.
Arthroscopy ; 32(2): 263-71, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26427632

RESUMO

PURPOSE: To (1) determine the length of the osteotomy at the anterior and posterior cortex, (2) compare between uni- and biplanar osteotomy, and (3) evaluate the relationship between the extent of the osteotomy and change of the posterior tibial slope. METHODS: A prospective comparative study of 24 uniplanar and 30 biplanar osteotomies was performed. To evaluate the length of osteotomy, osteotomy lines of the anterior and posterior cortex were analyzed in the 3-dimensional surface models. For slope measurement, the intramedullary axis of the proximal tibia (slope P), posterior cortical line of the proximal tibia (slope C), and anterior cortical line of the proximal fibula (slope F) were used. An analysis of the changes in the posterior tibial slope was performed independently using a pre- and postoperative lateral plane radiograph. RESULTS: In the uniplanar osteotomy, ratios of the osteotomized length to the total cortical length aligned with the osteotomized plane were larger in the anterior cortex (0.91 in uniplanar v 0.46 in biplanar; P = 0) and posterior cortex (0.97 in uniplanar v 0.79 ratio in biplanar; P = 0). Furthermore, the posterior tibial slope was maintained in both groups and the ratios between the anterior and posterior gap in both groups were 0.57 and 0.63, respectively. The maintenance of the slope was not related to any specific variables. Additionally, these phenomena did not differ between those patients who underwent uni- and those who underwent biplanar osteotomy. CONCLUSIONS: Increase in the posterior tibial slope was prevented with appropriate uni- or biplanar osteotomy with a simple distraction at the most posterior gap. However, in the uniplanar osteotomy, the ratio of the osteotomized length to the total cortical length was larger in both the anterior and posterior cortex.


Assuntos
Osteotomia/métodos , Tíbia/cirurgia , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Osteoartrite do Joelho/patologia , Osteoartrite do Joelho/cirurgia , Período Pós-Operatório , Estudos Prospectivos
14.
J Am Chem Soc ; 136(12): 4659-63, 2014 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-24580375

RESUMO

Lithium sulfide (Li2S) is an attractive cathode material with a high theoretical specific capacity (1166 mAh g(-1)). However, the poor cycle life and rate capability have remained significant challenges, preventing its practical application. Here, Li2S spheres with size control have been synthesized for the first time, and a CVD method for converting them into stable carbon-coated Li2S core-shell (Li2S@C) particles has been successfully employed. These Li2S@C particles with protective and conductive carbon shells show promising specific capacities and cycling performance with a high initial discharge capacity of 972 mAh g(-1) Li2S (1394 mAh g(-1) S) at the 0.2C rate. Even with no added carbon, a very high Li2S content (88 wt % Li2S) electrode composed of 98 wt % 1 µm Li2S@C spheres and 2 wt % binder shows rather stable cycling performance, and little morphology change after 400 cycles at the 0.5C rate.

15.
Phys Chem Chem Phys ; 16(32): 16931-40, 2014 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-24781200

RESUMO

Lithium/sulfur (Li/S) cells have attracted much attention due to their higher theoretical specific capacity and energy compared to those of current lithium-ion cells. However, the application of Li/S cells is still hampered by short cycle life. Sulfur-graphene oxide (S-GO) nanocomposites have shown promise as cathode materials for long-life Li/S cells because oxygen-containing functional groups on the surface of graphene oxide were successfully used as sulfur immobilizers by forming weak bonds with sulfur and polysulfides. While S-GO showed much improved cycling performance, the capacity decay still needs to be improved for commercially viable cells. In this study, we attempt to understand the capacity fading mechanism based on an ex situ study of the structural and chemical evolution of S-GO nanocomposite cathodes with various numbers of cycles using scanning electron microscopy (SEM), near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). It is found that both the surface morphologies and chemical structures of the cathode materials change considerably with increasing number of cycles. These changes are attributed to several unexpected chemical reactions of lithium with S-GO nanocomposites occurring during the discharge-charge processes with the formation of Li2CO3, Li2SO3, Li2SO4, and COSO2Li species. These reactions result in the loss of recyclable active sulfur on the surface of the electrode, and thus capacity fades while coulombic efficiency is near 100%. Moreover, the reaction products accumulate on the cathode surface, forming a compact blocking insulating layer which may make the diffusion of Li ions into/out of the cathode difficult during the discharge-charge process and thus lead to lower utilization of sulfur at higher rates. We think that these two observations are significant contributors to the capacity and rate capability degradation of the Li/S-GO cells. Therefore, for the rechargeable Li/S-GO cells, we suggest that the content of oxygen-containing functional groups on GO should be optimized and more stable functional groups need to be identified for further improvement of the cycling performance. The information we gain from this study may provide general insights into the fundamental understanding of the degradation mechanisms of other rechargeable Li/S cells using similar oxygen-containing functional groups as sulfur immobilizers.

16.
Nano Lett ; 13(12): 5891-9, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24219588

RESUMO

Lithium/sulfur (Li/S) cells are receiving significant attention as an alternative power source for zero-emission vehicles and advanced electronic devices due to the very high theoretical specific capacity (1675 mA·h/g) of the sulfur cathode. However, the poor cycle life and rate capability have remained a grand challenge, preventing the practical application of this attractive technology. Here, we report that a Li/S cell employing a cetyltrimethyl ammonium bromide (CTAB)-modified sulfur-graphene oxide (S-GO) nanocomposite cathode can be discharged at rates as high as 6C (1C = 1.675 A/g of sulfur) and charged at rates as high as 3C while still maintaining high specific capacity (~ 800 mA·h/g of sulfur at 6C), with a long cycle life exceeding 1500 cycles and an extremely low decay rate (0.039% per cycle), perhaps the best performance demonstrated so far for a Li/S cell. The initial estimated cell-level specific energy of our cell was ~ 500 W·h/kg, which is much higher than that of current Li-ion cells (~ 200 W·h/kg). Even after 1500 cycles, we demonstrate a very high specific capacity (~ 740 mA·h/g of sulfur), which corresponds to ~ 414 mA·h/g of electrode: still higher than state-of-the-art Li-ion cells. Moreover, these Li/S cells with lithium metal electrodes can be cycled with an excellent Coulombic efficiency of 96.3% after 1500 cycles, which was enabled by our new formulation of the ionic liquid-based electrolyte. The performance we demonstrate herein suggests that Li/S cells may already be suitable for high-power applications such as power tools. Li/S cells may now provide a substantial opportunity for the development of zero-emission vehicles with a driving range similar to that of gasoline vehicles.


Assuntos
Fontes de Energia Elétrica , Lítio/química , Enxofre/química , Grafite/química , Humanos , Emissões de Veículos
17.
Nat Nanotechnol ; 2024 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-38951597

RESUMO

The primary challenge facing silicon-based electronics, crucial for modern technological progress, is difficulty in dimensional scaling. This stems from a severe deterioration of transistor performance due to carrier scattering when silicon thickness is reduced below a few nanometres. Atomically thin two-dimensional (2D) semiconductors still maintain their electrical characteristics even at sub-nanometre scales and offer the potential for monolithic three-dimensional (3D) integration. Here we explore a strategic shift aimed at addressing the scaling bottleneck of silicon by adopting 2D semiconductors as new channel materials. Examining both academic and industrial viewpoints, we delve into the latest trends in channel materials, the integration of metal contacts and gate dielectrics, and offer insights into the emerging landscape of industrializing 2D semiconductor-based transistors for monolithic 3D integration.

18.
J Affect Disord ; 351: 381-386, 2024 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-38302064

RESUMO

BACKGROUND: We conducted a one-year, retrospective, mirror-image study to investigate the clinical effectiveness and safety of aripiprazole once monthly (AOM) in patients with bipolar disorder (BD). We compared pre-treatment conditions with outcomes after 12 months of AOM treatment. METHODS: Seventy-five bipolar patients were recruited from 12 hospitals in Korea. We included 75 patients with BD who had received at least three AOM treatments from September 2019 to September 2022 and had accessible electronic medical record (EMRs) for the year before and after the baseline visit. RESULTS: The overall number of mood episodes significantly decreased from a mean of 1.5 ± 1.2 episodes pre-AOM to 0.5 ± 1.2 episodes post-AOM. Manic episodes significantly decreased from 0.8 ± 0.8 episodes pre-AOM to 0.2 ± 0.5 episodes post-AOM, and depressive episodes significantly decreased from 0.5 ± 0.8 episodes pre-AOM to 0.2 ± 0.6 episodes post-AOM (p = 0.017). Moreover, the number of psychiatric medications and pills and the proportion of patients treated with complex polypharmacy were significantly decreased post-AOM. LIMITATIONS: The small sample size was insufficient to fully represent the entire population of individuals with BD, and potential selection bias was introduced due to only including subjects who received AOM three or more times. CONCLUSION: The results of this study suggest that AOM can reduce mood episode relapse and may be clinically beneficial in the treatment of BD patients, potentially reducing issues associated with polypharmacy in some individuals.


Assuntos
Antipsicóticos , Aripiprazol , Transtorno Bipolar , Humanos , Antipsicóticos/efeitos adversos , Aripiprazol/efeitos adversos , Transtorno Bipolar/tratamento farmacológico , Transtorno Bipolar/psicologia , Recidiva , Estudos Retrospectivos
19.
Nano Lett ; 12(12): 6474-9, 2012 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-23190038

RESUMO

With a theoretical capacity of 1166 mA·h·g(-1), lithium sulfide (Li(2)S) has received much attention as a promising cathode material for high specific energy lithium/sulfur cells. However, the insulating nature of Li(2)S prevents the achievement of high utilization (or high capacity) and good rate capability. Various efforts have been made to ameliorate this problem by improving the contact between Li(2)S and electronic conductors. In the literature, however, a relatively high capacity was only obtained with the Li(2)S content below 50 wt %; therefore, the estimated cell specific energy values are often below 350 W·h·kg(-1), which is insufficient to meet the ever-increasing requirements of newly emerging technologies. Here, we report a cost-effective way of preparing nanostructured Li(2)S-carbon composite cathodes by high-energy dry ball milling of commercially available micrometer-sized Li(2)S powder together with carbon additives. A simple but effective electrochemical activation process was used to dramatically improve the utilization and reversibility of the Li(2)S-C electrodes, which was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. We further improved the cycling stability of the Li(2)S-C electrodes by adding multiwalled carbon nanotubes to the nanocomposites. With a very high specific capacity of 1144 mA·h·g(-1) (98% of the theoretical value) obtained at a high Li(2)S content (67.5 wt %), the estimated specific energy of our cell was ∼610 W·h·kg(-1), which is the highest demonstrated so far for the Li/Li(2)S cells. The cells also maintained good rate capability and improved cycle life. With further improvement in capacity retention, nanostructured Li(2)S-C composite cathodes may offer a significant opportunity for the development of rechargeable cells with a much higher specific energy.

20.
Nano Lett ; 12(7): 3483-90, 2012 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-22681539

RESUMO

While pseudocapacitors represent a promising option for electrical energy storage, the performance of the existing ones must be dramatically enhanced to meet today's ever-increasing demands for many emerging applications. Here we report a nanostructured, mixed-valent manganese oxide film that exhibits anomalously high specific capacitance (∼2530 F/g of manganese oxide, measured at 0.61 A/g in a two-electrode configuration with loading of active materials ∼0.16 mg/cm(2)) while maintaining excellent power density and cycling life. The dramatic performance enhancement is attributed to its unique mixed-valence state with porous nanoarchitecture, which may facilitate rapid mass transport and enhance surface double-layer capacitance, while promoting facile redox reactions associated with charge storage by both Mn and O sites, as suggested by in situ X-ray absorption spectroscopy (XAS) and density functional theory calculations. The new charge storage mechanisms (in addition to redox reactions of cations) may offer critical insights to rational design of a new-generation energy storage devices.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA