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1.
Artigo em Inglês | MEDLINE | ID: mdl-32161128

RESUMO

The role of the crystal lattice for the electronic properties of cuprates and other high-temperature superconductors remains controversial despite decades of theoretical and experimental efforts. While the paradigm of strong electronic correlations suggests a purely electronic mechanism behind the insulator-to-metal transition, recently the mutual enhancement of the electron-electron and the electron-phonon interaction and its relevance to the formation of the ordered phases have also been emphasized. Here, we combine polarization-resolved ultrafast optical spectroscopy and state-of-the-art dynamical mean-field theory to show the importance of the crystal lattice in the breakdown of the correlated insulating state in an archetypal undoped cuprate. We identify signatures of electron-phonon coupling to specific fully symmetric optical modes during the buildup of a three-dimensional (3D) metallic state that follows charge photodoping. Calculations for coherently displaced crystal structures along the relevant phonon coordinates indicate that the insulating state is remarkably unstable toward metallization despite the seemingly large charge-transfer energy scale. This hitherto unobserved insulator-to-metal transition mediated by fully symmetric lattice modes can find extensive application in a plethora of correlated solids.

2.
Nat Commun ; 11(1): 850, 2020 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-32051405

RESUMO

In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exists to date at room temperature. In this work, we combine ultrafast broadband optical spectroscopy and advanced many-body calculations to reveal that organic-inorganic lead-bromide perovskites host Mahan excitons at room temperature. Persistence of the Wannier exciton peak and the enhancement of the above-bandgap absorption are observed at all achievable photoexcitation densities, well above the Mott density. This is supported by the solution of the semiconductor Bloch equations, which confirms that no sharp transition between the insulating and conductive phase occurs. Our results demonstrate the robustness of the bound states in a regime where exciton dissociation is otherwise expected, and offer promising perspectives in fundamental physics and in room-temperature applications involving high densities of charge carriers.

3.
Sci Adv ; 5(11): eaax2937, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31819899

RESUMO

Controlling the excitonic optical properties of room temperature semiconductors using time-dependent perturbations is key to future optoelectronic applications. The optical Stark effect in bulk and low-dimensional materials has recently shown exciton shifts below 20 meV. Here, we demonstrate dynamical tuning of the exciton properties by photoinduced coherent acoustic phonons in the cheap and abundant wide-gap semiconductor anatase titanium dioxide (TiO2) in single crystalline form. The giant coupling between the excitons and the photoinduced strain pulses yields a room temperature exciton shift of 30 to 50 meV and a marked modulation of its oscillator strength. An advanced ab initio treatment of the exciton-phonon interaction fully accounts for these results, and shows that the deformation potential coupling underlies the generation and detection of the giant acoustic phonon modulations.

4.
Science ; 364(6445): 1079-1082, 2019 06 14.
Artigo em Inglês | MEDLINE | ID: mdl-31197011

RESUMO

"Hidden phases" are metastable collective states of matter that are typically not accessible on equilibrium phase diagrams. These phases can host exotic properties in otherwise conventional materials and hence may enable novel functionality and applications, but their discovery and access are still in early stages. Using intense terahertz electric field excitation, we found that an ultrafast phase transition into a hidden ferroelectric phase can be dynamically induced in quantum paraelectric strontium titanate (SrTiO3). The induced lowering in crystal symmetry yields substantial changes in the phonon excitation spectra. Our results demonstrate collective coherent control over material structure, in which a single-cycle field drives ions along the microscopic pathway leading directly to their locations in a new crystalline phase on an ultrafast time scale.

5.
Acta Biomed ; 90(2): 251-258, 2019 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-31125004

RESUMO

BACKGROUND: Abdominal pain is the most frequent cause of hospital admission after Roux-en-y gastric bypass (RYGB). Among numerous possible underlying causes, internal hernias represent one of the most peculiar and insidious conditions, setting challenging diagnostic and therapeutic problems for the surgeon. The aim of this study is to analyze aspecific abdominal pain incidence and characteristics after RYGB, discriminating peculiar aspects suggestive of internal hernias. METHODS: 13 patients submitted to internal hernia repair after laparoscopic antecolic RYGB and a group of 49 controls (non-complicated RYGB) have been assessed using a specific questionnaire. Overall aspecific abdominal pain incidence and characteristics have been analysed. Typical pain traits and predisposing conditions for internal hernias have been investigated. RESULTS: 33% of controls reported aspecific abdominal pain after RYGB, mainly early postprandial, deep, remittent, colicky, located in the upper left abdomen. 77% of the case patients reported prodromal episodes of pain similar to the controls. The only significant differences between prodromal and acute episodes were pain intensity and quality (continuous). Excess weight lost at 3 months significantly correlated with internal hernia occurrence (p: 0.002). CONCLUSIONS: Based on abdominal pain characteristics, we can reasonably postulate the presence of remittent bowel torsions (remittent internal hernia) in many patients after antecolic RYGB, only occasionally complicating. Therapeutic management of these cases remains controversial, being laparoscopic exploration a reasonable option when symptomatology is suggestive.


Assuntos
Dor Abdominal/etiologia , Derivação Gástrica/efeitos adversos , Hérnia Abdominal/epidemiologia , Hérnia Abdominal/etiologia , Inquéritos e Questionários , Dor Abdominal/epidemiologia , Dor Abdominal/fisiopatologia , Adulto , Índice de Massa Corporal , Estudos de Casos e Controles , Feminino , Seguimentos , Derivação Gástrica/métodos , Hérnia Abdominal/fisiopatologia , Herniorrafia/efeitos adversos , Herniorrafia/métodos , Hospitais Universitários , Humanos , Incidência , Itália , Laparoscopia/efeitos adversos , Masculino , Pessoa de Meia-Idade , Obesidade Mórbida/cirurgia , Complicações Pós-Operatórias/epidemiologia , Complicações Pós-Operatórias/fisiopatologia , Medição de Risco
6.
Nano Lett ; 18(8): 5007-5014, 2018 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-30040906

RESUMO

The way nuclear motion affects electronic responses has become a very hot topic in materials science. Coherent acoustic phonons can dynamically modify optical, magnetic, and mechanical properties at ultrasonic frequencies, with promising applications as sensors and transducers. Here, by means of ultrafast broadband deep-ultraviolet spectroscopy, we demonstrate that coherent acoustic phonons confined in anatase TiO2 nanoparticles can selectively modulate the oscillator strength of the two-dimensional bound excitons supported by the material. We use many-body perturbation-theory calculations to reveal that the deformation potential is the mechanism behind the generation of the observed coherent acoustic wavepackets. Our results offer a route to manipulate and dynamically tune the properties of excitons in the deep-ultraviolet at room temperature.

7.
J Am Chem Soc ; 139(33): 11584-11589, 2017 08 23.
Artigo em Inglês | MEDLINE | ID: mdl-28762734

RESUMO

Ultrafast interfacial electron transfer in sensitized solar cells has mostly been probed by visible-to-terahertz radiation, which is sensitive to the free carriers in the conduction band of the semiconductor substrate. Here, we demonstrate the use of deep-ultraviolet continuum pulses to probe the interfacial electron transfer, by detecting a specific excitonic transition in both N719-sensitized anatase TiO2 and wurtzite ZnO nanoparticles. Our results are compared to those obtained on bare nanoparticles upon above-gap excitation. We show that the signal upon electron injection from the N719 dye into TiO2 is dominated by long-range Coulomb screening of the final states of the excitonic transitions, whereas in sensitized ZnO it is dominated by phase-space filling. The present approach offers a possible route to detecting interfacial electron transfer in a broad class of systems, including other transition metal oxides or sensitizers.

8.
Chimia (Aarau) ; 71(5): 288-294, 2017 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-28576155

RESUMO

We describe the facilities for ultraviolet studies in the femtosecond to nanosecond time domain. These facilities consist of: i) a set-up for deep-ultraviolet spectroscopy in the 260-380 nm range in both pump and probe pulses for transient absorption/reflectivity or two-dimensional spectroscopy studies; ii) a set-up for ultrafast fluorescence measurements with detection down to 300 nm. The capabilities of these set-ups are demonstrated by examples on molecular systems, biosystems, nanoparticles and solid materials.


Assuntos
Citocromos c/química , Mioglobina/química , Espectrofotometria Ultravioleta/instrumentação , Triptofano/química , Raios Ultravioleta , Animais , Coração , Cavalos , Fatores de Tempo
9.
Minerva Chir ; 72(4): 279-288, 2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28465502

RESUMO

BACKGROUND: The beneficial effects of bariatric surgery on diabetes and obesity have been widely demonstrated in the literature. The aim of our study was to evaluate the rate of failure of laparoscopic gastric bypass both in terms of weight loss and metabolic remission after one follow-up year. METHODS: A longitudinal, multicenter prospective study was carried out on 771 patients affected by pathological obesity. The following parameters were recorded for each patient before surgery: anthropometric, metabolic, social, smoking habits and previous failure of other bariatric procedures. After 1 follow-up year, final weight, final Body Mass Index (BMI), final percentage of lost excess body weight and percentage of lost BMI were evaluated. RESULTS: Statistical analysis showed a correlation between BMI>50 kg/m2, presence of metabolic syndrome, presence of diabetes, gastric pouch volume greater than 60 mL and failure of weight loss outcome. Statistical analysis of metabolic failure has recognized a high preoperative glycated hemoglobin percentage (HbA1c%) value as a statistically significant negative predictive factor. CONCLUSIONS: Bariatric Surgery is the most effective treatment for weight loss and metabolic improvement. However, in our study, surgery did not achieve the expected outcome in patients with specific metabolic, anthropometric and surgical characteristics (BMI>50 kg/m2, presence of metabolic syndrome, presence of T2DM with high preoperative HbA1c% level and gastric pouch volume greater than 60 mL).


Assuntos
Diabetes Mellitus Tipo 2/cirurgia , Derivação Gástrica , Laparoscopia , Obesidade Mórbida/cirurgia , Adulto , Idoso , Biomarcadores/urina , Índice de Massa Corporal , Diabetes Mellitus Tipo 2/complicações , Diabetes Mellitus Tipo 2/urina , Dislipidemias/complicações , Feminino , Seguimentos , Derivação Gástrica/métodos , Hemoglobina A Glicada/urina , Humanos , Itália , Laparoscopia/métodos , Estudos Longitudinais , Masculino , Síndrome Metabólica/cirurgia , Pessoa de Meia-Idade , Obesidade Mórbida/complicações , Estudos Prospectivos , Fatores de Risco , Fumar/efeitos adversos
10.
Struct Dyn ; 3(6): 064301, 2016 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-27990455

RESUMO

A femtosecond pump-probe setup is described that is optimised for broadband transient reflectivity experiments on solid samples over a wide temperature range. By combining high temporal resolution and a broad detection window, this apparatus can investigate the interplay between coherent collective modes and high-energy electronic excitations, which is a distinctive characteristic of correlated electron systems. Using a single-shot readout array detector at frame rates of 10 kHz allows resolving coherent oscillations with amplitudes <10-4. We demonstrate its operation on the charge-transfer insulator La2CuO4, revealing coherent phonons with frequencies up to 13 THz and providing access into their Raman matrix elements.

12.
Proc Natl Acad Sci U S A ; 112(46): 14212-7, 2015 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-26578765

RESUMO

Magnetic skyrmions are promising candidates as information carriers in logic or storage devices thanks to their robustness, guaranteed by the topological protection, and their nanometric size. Currently, little is known about the influence of parameters such as disorder, defects, or external stimuli on the long-range spatial distribution and temporal evolution of the skyrmion lattice. Here, using a large (7.3 × 7.3 µm(2)) single-crystal nanoslice (150 nm thick) of Cu2OSeO3, we image up to 70,000 skyrmions by means of cryo-Lorentz transmission electron microscopy as a function of the applied magnetic field. The emergence of the skyrmion lattice from the helimagnetic phase is monitored, revealing the existence of a glassy skyrmion phase at the phase transition field, where patches of an octagonally distorted skyrmion lattice are also discovered. In the skyrmion phase, dislocations are shown to cause the emergence and switching between domains with different lattice orientations, and the temporal fluctuation of these domains is filmed. These results demonstrate the importance of direct-space and real-time imaging of skyrmion domains for addressing both their long-range topology and stability.

13.
Obes Surg ; 25(11): 2040-6, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-25845353

RESUMO

BACKGROUND: Gastric bypass (GBP) is one of the most effective surgical procedures to treat morbid obesity and the related comorbidities. This study aimed at identifying preoperative predictors of successful weight loss and type 2 diabetes mellitus (T2DM) remission 1 year after GBP. METHODS: Prospective longitudinal study of 771 patients who underwent GBP was performed at four Italian centres between November 2011 and May 2013 with 1-year follow-up. Preoperative anthropometric, metabolic and social parameters, the surgical technique and the previous failed bariatric procedures were analyzed. Weight, the body mass index (BMI), the percentage of excess weight lost (% EWL), the percentage of excess BMI lost (% BMIL) and glycated haemoglobin (HbA1c) were recorded at follow-up. RESULTS: Univariate and multivariate analysis showed that BMI <50 kg/m(2) (p = 0.006) and dyslipidaemia (p = 0.05) were predictive factors of successful weight loss. Multivariate analysis of surgical technique showed significant weight loss in patients with a small gastric pouch (p < 0.001); the lengths of alimentary and biliary loops showed no statistical significance. All diabetic patients had a significant reduction of HbA1c (p < 0.001) after surgery. BMI ≥ 50 kg/m(2) (p = 0.02) and low level of preoperative HbA1c (p < 0.01) were independent risk factors of T2DM remission after surgery. CONCLUSIONS: This study provides a useful tool for making more accurate predictions of best results in terms of weight loss and metabolic improvement.


Assuntos
Glicemia/metabolismo , Derivação Gástrica , Obesidade Mórbida/diagnóstico , Obesidade Mórbida/cirurgia , Perda de Peso , Adulto , Idoso , Índice de Massa Corporal , Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/epidemiologia , Diabetes Mellitus Tipo 2/cirurgia , Feminino , Seguimentos , Derivação Gástrica/métodos , Hemoglobina A Glicada/metabolismo , Humanos , Estudos Longitudinais , Masculino , Pessoa de Meia-Idade , Obesidade Mórbida/sangue , Obesidade Mórbida/epidemiologia , Período Pré-Operatório , Prognóstico , Fatores de Risco , Adulto Jovem
14.
Obes Surg ; 24(2): 284-91, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24163189

RESUMO

BACKGROUND: The optimal dose of low molecular weight heparin (LMWH) to prevent venous thromboembolism (VTE) after bariatric surgery remains controversial. The aim of this multicentre, open-label, pilot study was to evaluate the efficacy and safety of two different doses of the LMWH parnaparin administered to patients undergoing bariatric surgery. METHODS: Patients were randomised to receive 4,250 IU/day (group A) or 6,400 IU/day (group B) of parnaparin s.c. for 7-11 days. Bilateral colour Doppler ultrasound of the lower limb was performed before surgery and at the end of the treatment period. The primary efficacy outcome was a composite of asymptomatic and symptomatic deep vein thrombosis, symptomatic pulmonary embolism and death from any cause during treatment. The primary safety endpoint was major and clinically relevant non-major bleeding. RESULTS: A total of 258 patients underwent randomization; 8 subjects were excluded following the safety analysis. One hundred thirty-one patients [106 females; mean age, 40.3 years (standard deviation (SD) ±9.6); mean body mass index (BMI), 44.6 kg/m(2) (SD ±5.4)] were assigned to group A and 119 patients [93 females; mean age, 41.5 years (SD ±9.9); mean BMI, 44.2 kg/m(2) (SD ±5.4)] were assigned to group B. The rate of the primary efficacy outcome was 1.5% (two cases; 95 % confidence interval (CI), 0.2-6.0%) in group A as compared with 0.8% (one case; 95% CI, 0.4-5.3%) in group B (p = ns). The composite incidence of major bleeding and clinically relevant non-major bleeding was 6.1% (eight cases; 95% CI, 2.9-12.1%) in group A and 5.0% (six cases; 95% CI, 2.1-11.1%) in group B (p = ns). CONCLUSIONS: A parnaparin dose of 4,250 IU/day seems suitable for VTE prevention in patients undergoing bariatric surgery.


Assuntos
Anticoagulantes/administração & dosagem , Cirurgia Bariátrica/efeitos adversos , Heparina de Baixo Peso Molecular/administração & dosagem , Obesidade Mórbida/cirurgia , Tromboembolia Venosa/prevenção & controle , Adulto , Relação Dose-Resposta a Droga , Esquema de Medicação , Feminino , Humanos , Masculino , Obesidade Mórbida/complicações , Obesidade Mórbida/tratamento farmacológico , Projetos Piloto , Pré-Medicação , Estudos Prospectivos , Resultado do Tratamento , Tromboembolia Venosa/tratamento farmacológico
15.
Thromb Res ; 124(5): e32-40, 2009 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-19744700

RESUMO

BACKGROUND: The treatment of venous thromboembolism (VTE) in cancer patients remains controversial. PURPOSE: The Italian Society for Thrombosis and Haemostasis (SISET) commissioned a project to develop clinical practice guidelines for the therapy of VTE in patients with malignancies. METHODS: Key questions about the treatment of VTE in patients with malignancies were formulated by a multidisciplinary working group consisting of experts in clinical medicine and research. After a systematic review and discussion of the literature, recommendations were formulated and graded according to the supporting evidence. For those questions for which the literature search did not yield any definitive answer (absence of evidence evidence of low quality, and contradictory evidence), a formal consensus method was used to issue clinical recommendations. RESULTS: The results of the available literature on VTE treatment in cancer patients were reviewed and clinical recommendations were drafted. CONCLUSION: We describe the results of a systematic literature review and an explicit approach to consensus techniques which resulted in recommendations for the key therapeutic issues in cancer patients with VTE.


Assuntos
Neoplasias/complicações , Tromboembolia Venosa/complicações , Tromboembolia Venosa/terapia , Humanos , Itália , Neoplasias/sangue , Resultado do Tratamento
16.
Thromb Res ; 124(6): 667-71, 2009 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-19482341

RESUMO

BACKGROUND: The optimal dose of low-molecular-weight-heparin (LMWH) to prevent venous thromboembolism (VTE) after bariatric surgery remains controversial. AIM: The aim of this study was to evaluate the pharmacodynamic parameters of two doses of the LMWH parnaparin administered to patients undergoing bariatric surgery. METHODS: Patients were enrolled in a multicentre, open label, pilot study and were randomised to receive 4250 IU/day [n=36; 30 females; median age: 38 years (23-56); median BMI: 46.7 Kg/m(2) (36.5-58.8)] or 6400 IU/day [n=30; 24 females; median age: 42 years (22-63); median BMI: 43.7 Kg/m(2) (36.1-64.1)] of parnaparin s.c. for 7-11 days. The pharmacodynamic effects of parnaparin were analysed by measuring the anti Factor Xa activity on day 0 (12 hours after the first parnaparin injection), day 4 and day 6 after surgery (before and 4 hours after parnaparin administration). RESULTS: In 98.3% of patients receiving 4250 IU/day the peak anti-Xa levels were in the range of 0.1-0.4 IU/ml. Higher anti-Xa levels were observed in patients receiving 6400 IU/day: in 62.3% of these patients the peak anti-Xa levels were greater than 0.4 IU/ml. The anti-Xa levels measured 4 hours after injection on days 4 and 6 were not statistically correlated with BMI for either dose of parnaparin (p=0.077 and p=0.401 for 4250 or 6400 IU/day, respectively). CONCLUSION: The dose of 4250 IU/day seems adequate to achieve prophylactic anti-Xa levels in morbid obese patients undergoing bariatric surgery. Conversely, most of the patients receiving 6.400 IU/day show anti-Xa levels higher than the recommended prophylactic values.


Assuntos
Cirurgia Bariátrica/métodos , Heparina de Baixo Peso Molecular/farmacologia , Tromboembolia Venosa/prevenção & controle , Adulto , Anticoagulantes/farmacologia , Inibidores do Fator Xa , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Complicações Pós-Operatórias/prevenção & controle , Estudos Prospectivos , Resultado do Tratamento
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