Exchange Interactions and High-Energy Spin States in Mn_12-acetate

We perform inelastic neutron scattering measurements on the molecular nanomagnet Mn_12-acetate to measure the excitation spectrum up to 45meV (500K). We isolate magnetic excitations in two groups at 5-6.5meV (60-75K) and 8-10.5meV (95-120K), with higher levels appearing only at 27meV (310K) and 31meV (360K). From a detailed characterization of the transition peaks we show that all of the low-energy modes appear to be separate S = 9 excitations above the S = 10 ground state, with the peak at 27meV (310K) corresponding to the first S = 11 excitation. We consider a general model for the four exchange interaction parameters of the molecule. The static susceptibility is computed by high-temperature series expansion and the energy spectrum, matrix elements and ground-state spin configuration by exact diagonalization. The theoretical results are matched with experimental observation by inclusion of cluster anisotropy parameters, revealing strong constraints on possible parameter sets. We conclude that only a model with dominant exchange couplings J_1 ~ J_2 ~ 5.5meV (65K) and small couplings J_3 ~ J_4 ~ 0.6meV (7K) is consistent with the experimental data.Comment: 17 pages, 12 figure

Heisenberg exchange parameters of molecular magnets from the high-temperature susceptibility expansion

We provide exact analytical expressions for the magnetic susceptibility function in the high temperature expansion for finite Heisenberg spin systems with an arbitrary coupling matrix, arbitrary single-spin quantum number, and arbitrary number of spins. The results can be used to determine unknown exchange parameters from zero-field magnetic susceptibility measurements without diagonalizing the system Hamiltonian. We demonstrate the possibility of reconstructing the exchange parameters from simulated data for two specific model systems. We examine the accuracy and stability of the proposed method.Comment: 13 pages, 7 figures, submitted to Phys. Rev.

High resolution propagation-based imaging system for in vivo dynamic computed tomography of lungs in small animals

We have developed an x-ray imaging system for in vivo four-dimensional computed tomography (4DCT) of small animals for pre-clinical lung investigations. Our customized laboratory facility is capable of high resolution in vivo imaging at high frame rates. Characterization using phantoms demonstrate a spatial resolution of slightly below 50 μm at imaging rates of 30 Hz, and the ability to quantify material density differences of at least 3%. We benchmark our system against existing small animal pre-clinical CT scanners using a quality factor that combines spatial resolution, image noise, dose and scan time. In vivo 4DCT images obtained on our system demonstrate resolution of important features such as blood vessels and small airways, of which the smallest discernible were measured as 55-60 μm in cross section. Quantitative analysis of the images demonstrate regional differences in ventilation between injured and healthy lungs.M. Preissner , R. P. Murrie, I. Pinar, F. Werdiger, R. P. Carnibella, G. R. Zosky, A. Fouras and S. Dubsk

Eyewitness Testimony in Autism Spectrum Disorder: A Review

Autism spectrum disorder (ASD) is estimated to affect around 1% of the population, and is characterised by impairments in social interaction, communication, and behavioural flexibility. A number of risk factors indicate that individuals with ASD may become victims or witnesses of crimes. In addition to their social and communication deficits, people with ASD also have very specific memory problems, which impacts on their abilities to recall eyewitnessed events. We begin this review with an overview of the memory difficulties that are experienced by individuals with ASD, before discussing the studies that have specifically examined eyewitness testimony in this group and the implications for investigative practice. Finally, we outline related areas that would be particularly fruitful for future research to explore

Energy intakes of children after preloads: adjustment, not compensation

Background: Young children accurately compensate for energy-dense preloads consumed before test meals. The accuracy of compensation seems to deteriorate as a function of age.Objective: The hypothesis that accurate energy compensation varies by age, body mass index, and individual characteristics of children and their mothers was tested. Design: Energy intake (EI) from a test meal was measured in 74 children aged 6-9 y 90 min after the ingestion of no-energy (NE), low-energy (LE), or high-energy (HE) preload snacks. The NE preload consisted of 250 mL water, the LE preload consisted of a 56-g muffin + a 250-mL orange drink (783 kJ), and the HE preload consisted of a 56-g muffin + a 250-mL orange drink (1628 W).Results: A significant dose-related reduction in El was found after the preloads; younger children adjusted more effectively than did older children, although total El (including preload energy) indicated that the adjustment was not accurate. The compensation index (COMPX) differed by preload and age group; COMPX scores were higher between the NE and LE preloads (younger children: 44.4 9.3%; older children: 57.0 +/- 11.6%) than between the NE and HE preloads (39.6 +/- 4.9%; 31.3 +/- 6.2%) and the LE and HE preloads (35.2 +/- 7.8%; 7.4 +/- 9.8%). This finding indicates a more consistent response across preloads and a greater sensitivity to energy load by younger than by older children. High interindividual variation and low intraindividual variation in COMPX was found. The tendency to over- or undereat in response to the preloads (deviation from perfect) correlated directly and positively with maternal concerns about child overweight, not with actual BMI.Conclusions: The children adjusted their EIs in response to different preloads, and the younger children did so more effectively than did the older children. Poor short-term energy compensation may constitute a behavioral marker for positive energy balance.</p

Variants of the peroxisome proliferator-activated receptor g- and b-adrenergic receptor genes are associated with measures of compensatory eating behaviors in young children.

Background: Young children can regulate energy precisely in the short term, showing the potential for an innate compensation mechanism of eating behavior. However, data suggest that precise compensation is attenuated as a function of increasing adiposity, parental feeding style, and age.Commonvariation in candidate obesity genes may account for some of the individual variation observed in shortterm energy compensation. Polymorphisms in the peroxisome proliferator-activated receptor (PPARG) and -adrenergic receptor (ADRB3) genes have been linked to increased body mass index (BMI; in kg/m2), obesity, and more recently dietary nutrients and preferences. In addition, common variation in ADRB3 interacts with PPARG to modulate adult body weight. Objective: This study investigated whether variants in these genes were associated with measurable effects on child eating behavior. Design: Children (n 84) aged 4–10 y were prospectively selected for variants of the PPARG locus (Pro12Ala, C1431T). Heights and weights were measured. Energy intake from a test meal was measured 90 min after ingestion of a no-energy (NE), low-energy (LE), or high-energy (HE) preload, and the compensation index(COMPX) was calculated. Results: BMI differed significantly by gene model, whereby Pro12Ala was associated with a lower BMI. Poor COMPX was associated with the PPARG T1431 allele (P 0.009). There was a significant interaction between COMPX and the ADRB3 Trp64Arg variant in modulating compensation (P 0.003), whereas the Arg64 allele was associated with good compensation (P 0.001). Conclusions: This is the first study to suggest that a genetic interaction involving ADRB3 and PPARG variants influences eating behavior in children

Gadolinium-doped magnetite nanoparticles from a single-source precursor

An iron and gadolinium-containing bimetallic polynuclear complex was used as a single source precursor in the synthesis of gadolinium-doped magnetite nanoparticles (Gd:Fe3O4). The synthesis produces well defined octahedral particles (12.6 ± 2.6 nm diameter) with a gadolinium content in the region of 2 mol%. The nanoparticles showed a value of the Specific Absorption Rate of 3.7 ± 0.6 W / gFe under low-amplitude radiofrequency magnetic field excitation, and moderate biocompatibility, suggesting that these particles are viable candidates for Magnetic Hyperthermia applications