Mechanisms behind the enhancement of thermal properties of graphene nanofluids.

While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π-π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties.

Graphene-based synthetic antiferromagnets and ferrimagnets.

Graphene-spaced magnetic systems with antiferromagnetic exchange-coupling offer exciting opportunities for emerging technologies. Unfortunately, the in-plane graphene-mediated exchange-coupling found so far is not appropriate for realistic exploitation, due to being weak, being of complex nature, or requiring low temperatures. Here we establish that ultra-thin Fe/graphene/Co films grown on Ir(111) exhibit robust perpendicular antiferromagnetic exchange-coupling, and gather a collection of magnetic properties well-suited for applications. Remarkably, the observed exchange coupling is thermally stable above room temperature, strong but field controllable, and occurs in perpendicular orientation with opposite remanent layer magnetizations. Atomistic first-principles simulations provide further ground for the feasibility of graphene-spaced antiferromagnetic coupled structures, confirming graphene's direct role in sustaining antiferromagnetic superexchange-coupling between the magnetic films. These results provide a path for the realization of graphene-based perpendicular synthetic antiferromagnetic systems, which seem exciting for fundamental nanoscience or potential use in spintronic devices.Antiferromagnetic spintronics may pave the way to innovative information storage devices with perpendicular coupling, however experimental demonstrations are still sparse. Here, the authors demonstrate a graphene-mediated perpendicular antiferromagnetic coupling between Fe and Co layers in a Fe/graphene/Co sandwich structure.

Theoretical study on the influence of the Mg2+ and Al3+ octahedral cations on the vibrational spectra of the hydroxy groups of dioctahedral 2:1 phyllosilicate models.

The effect on the vibrational spectrum of the hydroxy groups in dioctahedral 2:1 phyllosilicates of the isomorphous cation substitution of Mg(2+) by Al(3+) in the octahedral sheet was investigated at the DFT level. Ortho, meta and para Mg(2+) configurational polymorphs were defined. The theoretical vibration frequencies of OH groups depend significantly on the nature of the cations they are joined with. Theoretical values are spread out over narrow ranges: 3,612-3,626 cm(-1) for ν(AlOHMg), 3,604-3,606 cm(-1) for ν(AlOHAl), and 3,657-3,660 cm(-1) for ν(MgOHMg); 803-830 cm(-1) for δ(AlOHMg), 877 cm(-1) for δ(AlOHAl), and 693-711 cm(-1) for δ(MgOHMg), in agreement with known experimental values. From the intensities of the XOHY bands, we observe that the vibrational adsorptivities of the ν(OH) vibrations are not the same for all XOHY groups, and that ν(MgOHMg) absorptivity is much lower than that of ν(AlOHAl). These theoretical results should be taken into account in quantitative analysis of experimental vibrational studies in clay minerals, introducing different molar extinction coefficients in the Lambert-Beer law to determine the relative concentrations of both cationic arrangements.

Diminished alveolar microvascular reserves in type 2 diabetes reflect systemic microangiopathy.

OBJECTIVE: Alveolar microvascular function is moderately impaired in type 1 diabetes, as manifested by restriction of lung volume and diffusing capacity (DL(CO)). We examined whether similar impairment develops in type 2 diabetes and defined the physiologic sources of impairment as well as the relationships to glycemia and systemic microangiopathy. RESEARCH DESIGN AND METHODS: A cross-sectional study was conducted at a university-affiliated diabetes treatment center and outpatient diabetes clinic, involving 69 nonsmoking type 2 diabetic patients without overt cardiopulmonary disease. Lung volume, pulmonary blood flow (Q), DL(CO), membrane diffusing capacity (measured from nitric oxide uptake [DL(NO)]), and pulmonary capillary blood volume (V(C)) were determined at rest and exercise for comparison with those in 45 healthy nonsmokers as well as with normal reference values. RESULTS: In type 2 diabetic patients, peak levels of oxygen uptake, Q and DL(CO), DL(NO), and V(C) at exercise were 10-25% lower compared with those in control subjects. In nonobese patients (BMI <30 kg/m(2)), reductions in DL(CO), DL(NO), and V(C) were fully explained by the lower lung volume and peak Q, but these factors did not fully explain the impairment in obese patients (BMI >30 kg/m(2)). The slope of the increase in V(C) with respect to Q was reduced approximately 20% in patients regardless of BMI, consistent with impaired alveolar-capillary recruitment. Functional impairment was directly related to A1C level, retinopathy, neuropathy, and microalbuminuria in a sex-specific manner. CONCLUSIONS: Alveolar microvascular reserves are reduced in type 2 diabetes, reflecting restriction of lung volume, alveolar perfusion, and capillary recruitment. This reduction correlates with glycemic control and extrapulmonary microangiopathy and is aggravated by obesity.

Obesity-independent hyperinsulinemia in nondiabetic first-degree relatives of individuals with type 2 diabetes.

A close association between obesity and hyperinsulinemia is well recognized, but it is not known whether this relationship is affected by the genetic susceptibility to type 2 diabetes. Insulin response to a 75-g oral glucose load was evaluated in healthy nondiabetic Caucasians with first-degree family history of diabetes (relatives, n = 55) and those without family history (nonrelatives, n = 33). A significant correlation between the BMI and insulin response (area under the curve [AUC] during the 2-h period) was seen in nonrelatives (r = 0.68, P < 0.0001) but not in the relatives (r = 0.12, P = 0.37). Multivariate analysis revealed that obesity (BMI) was the primary determinant of insulin response in nonrelatives (P < 0.001), whereas among the relatives, BMI had no significant impact (P = 0.28). Thus, these distinctions between the relatives and nonrelatives remained after adjusting for glucose level, age, and gender. Among first-degree relatives, the commonly observed association between BMI and insulin response is lost, and hyperinsulinemia is present even in the absence of obesity. First-degree family history of diabetes may confer insulin resistance that is independent of obesity. Alternatively, this could suggest a pathological regulation of an obesity-insulin feedback loop, e.g., a defective recognition of adiposity.