Bound states and field-polarized Haldane modes in a quantum spin ladder

The challenge of one-dimensional systems is to understand their physics beyond the level of known elementary excitations. By high-resolution neutron spectroscopy in a quantum spin ladder material, we probe the leading multiparticle excitation by characterizing the two-magnon bound state at zero field. By applying high magnetic fields, we create and select the singlet (longitudinal) and triplet (transverse) excitations of the fully spin-polarized ladder, which have not been observed previously and are close analogs of the modes anticipated in a polarized Haldane chain. Theoretical modelling of the dynamical response demonstrates our complete quantitative understanding of these states.Comment: 6 pages, 3 figures plus supplementary material 7 pages 5 figure

Prognostic Value of E/E′ Ratio in Patients With Unoperated Severe Aortic Stenosis

ObjectivesThe aim of this study was to evaluate the value of clinical and echo-Doppler parameters for the prognosis of unoperated severe aortic stenosis (AS).BackgroundApproximately one-third of severe, symptomatic AS patients are denied surgery. Risk stratification of unoperated AS is important to determine eligibility for percutaneous aortic valve replacement, an evolving treatment option for AS patients deemed suboptimal for surgical aortic valve replacement.MethodsWe retrospectively compared clinical and echo-Doppler parameters between survivors and nonsurvivors of 125 patients with unoperated severe AS.ResultsThe 1-year survival rate was 62.4%. In univariate analysis, survivors compared with nonsurvivors were younger (80.0 ± 10.9 years vs. 84.9 ± 11.1 years, p = 0.02), had a greater left ventricular ejection fraction (LVEF) (55 ± 15% vs. 50 ± 16%, p = 0.042), a higher left ventricular stroke volume (63 ± 19 ml vs. 56 ± 13 ml, p = 0.015), a lower E/E′ ratio (12.19 ± 5.7 vs. 16.87 ± 7.43, p < 0.001), and a lower prevalence of E/E′ >15 (20% vs. 55%, p < 0.001). Symptomatic status was nonsignificantly different between survivors and nonsurvivors. In patients with an LVEF ≥50%, the subgroup with E/E′ ≤15 and with E/E′ >15 had a 73.8% and 47.8% 1-year survival rate, respectively (p = 0.027). In the patients with an LVEF <50%, the patients with E/E′ ≤15 and those with E/E′ >15 demonstrated a 70.6% and 22.3% 1-year survival rate, respectively (p = 0.003). In multivariate analysis, significant predictors of mortality were E/E′ >15 and a combination of E/E′ >15 and B-type natriuretic peptide >300 ng/ml: adjusted mortality risk 2.34 (95% confidence interval (CI) 1.27 to 4.33, p = 0.0072) and 2.59 (95% CI 1.21 to 5.55, p = 0.014), respectively.ConclusionsThe E/E′ ratio is the single most predictive clinical and echo-Doppler parameter in the assessment of overall prognosis in patients with unoperated severe AS. LVEF was a significant predictor of survival only in the univariate analysis. B-type natriuretic peptide alone was not a predictor of prognosis in the study population. However, the combination of E/E′ and B-type natriuretic peptide is even more predictive of the 1-year prognosis

Thermodynamics of the Spin Luttinger-Liquid in a Model Ladder Material

The phase diagram in temperature and magnetic field of the metal-organic, two-leg, spin-ladder compound (C5H12N)2CuBr4 is studied by measurements of the specific heat and the magnetocaloric effect. We demonstrate the presence of an extended spin Luttinger-liquid phase between two field-induced quantum critical points and over a broad range of temperature. Based on an ideal spin-ladder Hamiltonian, comprehensive numerical modelling of the ladder specific heat yields excellent quantitative agreement with the experimental data across the complete phase diagram.Comment: 4 pages, 4 figures, updated refs and minor changes to the text, version accepted for publication in Phys. Rev. Let

Field-controlled magnetic order in the quantum spin-ladder system (Hpip)2CuBr4

International audienceNeutron diffraction is used to investigate the field-induced, antiferromagnetically ordered state in the two-leg spin-ladder material (Hpip)2CuBr4. This “classical” phase, a consequence of weak interladder coupling, is nevertheless highly unconventional: its properties are influenced strongly by the spin Luttinger-liquid state of the ladder subunits. We determine directly the order parameter (transverse magnetization), the ordering temperature, the spin structure, and the critical exponents around the transition. We introduce a minimal microscopic model for the interladder coupling and calculate the quantum fluctuation corrections to the mean-field interaction

Surface-initiated growth of copper using isonicotinic acid-functionalized aluminum oxide surfaces

Isonicotinate self-assembled monolayers (SAM) were prepared on alumina surfaces (A) using isonicotinic acid (iNA). These functionalized layers (iNA-A) were used for the seeded growth of copper films (Cu-iNA-A) by hydrazine hydrate-initiated electroless deposition. The films were characterized by scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and advancing contact angle measurements. The films are Cu0 but with surface oxidation, and show a faceted morphology, which is more textured (Rq = 460 ± 90 nm) compared to the SAM (Rq = 2.8 ± 0.5 nm). In contrast, growth of copper films by SnCl2/PdCl2 catalyzed electroless deposition, using formaldehyde (CH2O) as the reducing agent, shows a nodular morphology on top of a relatively smooth surface. No copper films are observed in the absence of the isonicotinate SAM. The binding of Cu2+ to the iNA is proposed to facilitate reduction to Cu0 and create the seed for subsequent growth. The films show good adhesion to the functionalized surface

Durable vesicles for reconstitution of membrane proteins in biotechnology

The application of membrane proteins in biotechnology requires robust, durable reconstitution systems that enhance their stability and support their functionality in a range of working environments. Vesicular architectures are highly desirable to provide the compartmentalisation to utilise the functional transmembrane transport and signalling properties of membrane proteins. Proteoliposomes provide a native-like membrane environment to support membrane protein function, but can lack the required chemical and physical stability. Amphiphilic block copolymers can also self-assemble into polymersomes: tough vesicles with improved stability compared with liposomes. This review discusses the reconstitution of membrane proteins into polymersomes and the more recent development of hybrid vesicles, which blend the robust nature of block copolymers with the biofunctionality of lipids. These novel synthetic vesicles hold great promise for enabling membrane proteins within biotechnologies by supporting their enhanced in vitro performance and could also contribute to fundamental biochemical and biophysical research by improving the stability of membrane proteins that are challenging to work with

Sources of avoidance motivation: Valence effects from physical effort and mental rotation

When reaching goals, organisms must simultaneously meet the overarching goal of conserving energy. According to the law of least effort, organisms will select the means associated with the least effort. The mechanisms underlying this bias remain unknown. One hypothesis is that organisms come to avoid situations associated with unnecessary effort by generating a negative valence toward the stimuli associated with such situations. Accordingly, merely using a dysfunctional, ‘slow’ computer mouse causes participants to dislike ambient neutral images (Study 1). In Study 2, nonsense shapes were liked less when associated with effortful processing (135° of mental rotation) versus easier processing (45° of rotation). Complementing ‘fluency’ effects found in perceptuo-semantic research, valence emerged from action-related processing in a principled fashion. The findings imply that negative valence associations may underlie avoidance motivations, and have practical implications for educational/workplace contexts in which effort and positive affect are conducive to success