Bosonic representation of one-dimensional Heisenberg ferrimagnets

The energy structure and the thermodynamics of ferrimagnetic Heisenberg chains of alternating spins S and s are described in terms of the Schwinger bosons and modified spin waves. In the Schwinger representation, we average the local constraints on the bosons and diagonalize the Hamiltonian at the Hartree-Fock level. In the Holstein-Primakoff representation, we optimize the free energy in two different ways introducing an additional constraint on the staggered magnetization. A new modified spin-wave scheme, which employs a Lagrange multiplier keeping the native energy structure free from temperature and thus differs from the original Takahashi Scheme, is particularly stressed as an excellent language to interpret one-dimensional quantum ferrimagnetism. Other types of one-dimensional ferrimagnets and the antiferromagnetic limit S=s are also mentioned.Comment: to be published in Phys. Rev. B 69, No. 6, 0644XX (2004

Fast and robust 3-D MRI brain structure segmentation

We present a novel method for the automatic detection and segmentation of (sub-)cortical gray matter structures in 3-D magnetic resonance images of the human brain. Essentially, the method is a topdown segmentation approach based on the recently introduced concept of Marginal Space Learning (MSL). We show that MSL naturally decomposes the parameter space of anatomy shapes along decreasing levels of geometrical abstraction into subspaces of increasing dimensionality by exploiting parameter invariance. At each level of abstraction, i.e., in each subspace, we build strong discriminative models from annotated training data, and use these models to narrow the range of possible solutions until a final shape can be inferred. Contextual information is introduced into the system by representing candidate shape parameters with high-dimensional vectors of 3-D generalized Haar features and steerable features derived from the observed volume intensities. Our system allows us to detect and segment 8 (sub-)cortical gray matter structures in T1-weighted 3-D MR brain scans from a variety of different scanners in on average 13.9 sec., which is faster than most of the approaches in the literature. In order to ensure comparability of the achieved results and to validate robustness, we evaluate our method on two publicly available gold standard databases consisting of several T1-weighted 3-D brain MR scans from different scanners and sites. The proposed method achieves an accuracy better than most state-of-the-art approaches using standardized distance and overlap metrics.Michael Wels, Yefeng Zheng, Gustavo Carneiro, Martin Huber, Joachim Hornegger and Dorin Comanici

New polymers for drug delivery systems in orthopaedics: in vivo biocompatibility evaluation

The use of biodegradable polymers for drug delivery systems excluded the need for a second operation to remove the carrier. However, the development of an avascular fibrous capsule, reducing drug release, has raised concern about these polymers in terms of tissue-implant reaction. Five novel polymers were evaluated in vivo after implantation in the rat dorsal subcutis and compared to the reference polycaprolactone (PCL). Poly(cyclohexyl-sebacate) (PCS), poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) (PLLA-PDXO-PLLA), two 3-hydroxybutyrate-co-3-hydroxyvalerate copolymers (D400G and D600G), and a poly(organo)phosphazene (POS-PheOEt:Imidazole) specimens were histologically evaluated in terms of the inflammatory tissue thickness and vascular density at 4 and 12 weeks from surgery. The highest values of inflammatory tissue thickness were observed in D600G (P < 0.01), PCS (P < 0.001) and PLLA-PDXO-PLLA (P < 0.001) at 4 weeks, while POP - PheOEt:Imidazole showed the lowest value of inflammatory tissue thickness (P < 0.05) at 12 weeks. D400G, D600G, PLLA-PDXO-PPLA and POP - PheOEt:Imidazole showed higher (P < 0.001) values of vascular density near the implants in comparison to PCL at 4 weeks. Finally, D400G and D600G increased their vessel densities while POP - PheOEt:Imidazole and the synthetic polyester PLLA-PDXO-PLLA presented similar vessel density values during experimental times. These different behaviours to improve neoangiogenesis without severe inflammatory tissue-responses could be further investigated with drugs in order to obtain time-programmable drug delivery systems for musculoskeletal therapy

Household bushmeat consumption in Brazzaville, the Republic of the Congo.

Wildlife meat is an important source of animal protein for rural and urban populations in Congo. Quantitative and qualitative surveys on the consumption of bushmeat were undertaken in Brazzaville in 2006, in about 1,050 urban households. The main objective was to establish the profiles of consumers and of species concerned. The results showed that 88.3% of the surveyed households consumed bushmeat. Their average size was 5.7 ± 3.2 persons. The average monthly income of an urban consumer with a permanent job was 98,334 (US$197) ± 84,306 (US$169) FCFA. It appeared that households preferred to consume bushmeat for two major reasons: the taste or flavor (67.8%) and food habits (14.7%). Meat from mammals was preferred, the top three orders of this class being artiodactyls (48.3%), rodents (28.3%), and primates (13.0%). Some of them are listed as threatened in Congo Brazzaville and are included in the IUCN Red List. The results showed that in Brazzaville, bushmeat consumption remains important and is determined by socio-economic parameters. The promotion of game farming, and breeding of domestic species such as poultry and fish, in the Brazzaville suburbs could help to meet Congolese demand for bushmeat