94 research outputs found
Impact of disorder on optical phonons confined in CdS nano-crystallites embedded in a SiO2 matrix
Non-resonant Raman spectroscopy studies of a set of CdS films annealed at different temperatures were performed and showed a direct correlation between the width of the Raman peak produced by CdS-like optical phonons and the crystalline quality of the semiconductor phase probed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). In order to decribe the
Raman lineshape a model proposed by Trallero-Giner et al (1998 Phys. Rev.
B 57 4664) was used, which considers optical phonons confined in small semiconductor spheres with a size distribution. The model is shown to give a
good reproduction of the spectra of samples where the semiconductor phase is
most crystalline. However, it required too large values of phonon damping to fit
the spectra of several other samples, which, according to XRD and TEM data, do contain CdS nano-crystallites. This large broadening of the Raman peak was considered as inhomogeneous, i.e. associated with disorder. Numerical lattice dynamics calculations were performed for 2D binary clusters of arbitrary
shape and three kinds of disorder were considered, (i) random variation of
the Cd–S bond frequency from one nano-crystallite to another, (ii) cluster shape irregularities and (iii) fluctuations of the nearest-neighbour interaction constant within one cluster. It is shown that ‘ensemble disorder’ (i) can be responsible for a shoulder above the bulk CdS phonon frequency observed for some of our samples. The effect of shape disorder (ii) is similar to that of the size dispersion producing some inhomogeneous broadening of the peak. In
addition, it gives rise to an extra low-frequency mode originating from the top
of the acoustic band. The force constant’s disorder (iii) is shown to result in a stronger asymmetric broadening of the Raman peak.Fundação para a Ciência e a Tecnologia (FCT
Identification of potential prognostic biomarkers for node-negative breast tumours by proteomic analysis: a multicentric 2004 national PHRC study
We used a 2D-electrophoresis (2-DE) proteomic approach to identify novel biomarkers in node-negative breast cancers. This retrospective study focused on a population of patients with ductal pN0M0 tumours. A subset of patients who developed metastases and in whose tumours were found high levels of uPA and PAI-1 (metastatic relapse, MR: n=20) were compared to another subset in whom no metastatic relapse occurred and whose tumours were found to have low levels of uPA and PAI-1 (no relapse, NR: n=21). We used a 2-DE coupled with MS approach to screen cytosol fractions using two pH-gradient scales, a broad scale (3.0-11.0) and a narrower scale focussing in on a protein rich region (5.0-8.0). This study was conducted on 41 cytosol specimens analyzed in duplicate on two platforms. The differential analysis of more than 2,000 spots in 2-DE gels, obtained on the two platforms, allowed the identification of 13 proteins which were confirmed by western blotting. Two proteins, GPDA and FABP4 were down-regulated in the MR subset whereas all the others were up-regulated. An in silico analysis revealed that GMPS (GUAA), GAPDH (G3P), CFL1 (COF1) and FTL (FRIL), the most informative genes, displayed a proliferation profile (high expression in basal-like, HER2+ and luminal B molecular subtypes). Inversely, similar to FABP4, GPD1 [GPDA] displayed a high expression in luminal A subtype, a profile characteristic of tumour suppressor genes. Despite the small size of our cohort, the 2-DE analysis gave interesting results which were confirmed by the in silico analysis showing that some of the corresponding genes had a strong prognostic impact in breast cancer, mostly because of their link with proliferation: GMPS, GAPDH, FTL and GPD1. A validation phase on a larger cohort is now needed before these biomarkers could be considered for use in clinical practice
Surface induced disorder in body-centered cubic alloys
We present Monte Carlo simulations of surface induced disordering in a model
of a binary alloy on a bcc lattice which undergoes a first order bulk
transition from the ordered DO3 phase to the disordered A2 phase. The data are
analyzed in terms of an effective interface Hamiltonian for a system with
several order parameters in the framework of the linear renormalization
approach due to Brezin, Halperin and Leibler. We show that the model provides a
good description of the system in the vicinity of the interface. In particular,
we recover the logarithmic divergence of the thickness of the disordered layer
as the bulk transition is approached, we calculate the critical behavior of the
maxima of the layer susceptibilities, and demonstrate that it is in reasonable
agreement with the simulation data. Directly at the (110) surface, the theory
predicts that all order parameters vanish continuously at the surface with a
nonuniversal, but common critical exponent. However, we find different
exponents for the order parameter of the DO3 phase and the order parameter of
the B2 phase. Using the effective interface model, we derive the finite size
scaling function for the surface order parameter and show that the theory
accounts well for the finite size behavior of the DO3 ordering but not for that
of B2 ordering. The situation is even more complicated in the neighborhood of
the (100) surface, due to the presence of an ordering field which couples to
the B2 order.Comment: To appear in Physical Review
Electronic structure and optical properties of ZnS/CdS nanoheterostructures
The electronic and optical properties of spherical nanoheterostructures are
studied within the semi-empirical tight-binding model including
the spin-orbit interaction. We use a symmetry-based approach previously applied
to CdSe and CdTe quantum dots. The complete one-particle spectrum is obtained
by using group-theoretical methods. The excitonic eigenstates are then deduced
in the configuration-interaction approach by fully taking into account the
Coulomb direct and exchange interactions. Here we focus on ZnS/CdS, ZnS/CdS/ZnS
and CdS/ZnS nanocrystals with particular emphasis on recently reported
experimental data. The degree of carrier localization in the CdS well layer is
analyzed as a function of its thickness. We compute the excitonic fine
structure, i.e., the relative intensities of low-energy optical transitions.
The calculated values of the absorption gap show a good agreement with the
experimental ones. Enhanced resonant photoluminescence Stokes shifts are
predicted.Comment: 6 pages, 4 Figures, revtex
Pooled analysis of prognostic impact of urokinase-type plasminogen activator and its inhibitor PAI-1 in 8377 breast cancer patients
BACKGROUND: Urokinase-type plasminogen activator (uPA) and its inhibitor
(PAI-1) play essential roles in tumor invasion and metastasis. High levels
of both uPA and PAI-1 are associated with poor prognosis in breast cancer
patients. To confirm the prognostic value of uPA and PAI-1 in primary
breast cancer, we reanalyzed individual patient data provided by members
of the European Organization for Research and Treatment of Cancer-Receptor
and Biomarker Group (EORTC-RBG). METHODS: The study included 18 datasets
involving 8377 breast cancer patients. During follow-up (median 79
months), 35% of the patients relapsed and 27% died. Levels of uPA and
PAI-1 in tumor tissue extracts were determined by different immunoassays;
values were ranked within each dataset and divided by the number of
patients in that dataset to produce fractional ranks that could be
compared directly across datasets. Associations of ranks of uPA and PAI-1
levels with relapse-free survival (RFS) and overall survival (OS) were
analyzed by Cox multivariable regression analysis stratified by dataset,
including the following traditional prognostic variables: age, menopausal
status, lymph node status, tumor size, histologic grade, and steroid
hormone-receptor status. All P values were two-sided. RESULTS: Apart from
lymph node status, high levels of uPA and PAI-1 were the strongest
predictors of both poor RFS and poor OS in the analyses of all patients.
Moreover, in both lymph node-positive and lymph node-negative patients,
higher uPA and PAI-1 values were independently associated with poor RFS
and poor OS. For (untreated) lymph node-negative patients in particular,
uPA and PAI-1 included together showed strong prognostic ability (all
P<.001). CONCLUSIONS: This pooled analysis of the EORTC-RBG datasets
confirmed the strong and independent prognostic value of uPA and PAI-1 in
primary breast cancer. For patients with lymph node-negative breast
cancer, uPA and PAI-1 measurements in primary tumors may be especially
useful for designing individualized treatment strategies
Postoperative serum proteomic profiles may predict recurrence-free survival in high-risk primary breast cancer
Item does not contain fulltextPURPOSE: Better breast cancer prognostication may improve selection of patients for adjuvant therapy. We conducted a retrospective longitudinal study in which we investigated sera of high-risk primary breast cancer patients, to search for proteins predictive of recurrence-free survival. METHODS: Sera of 82 breast cancer patients obtained after surgery, but prior to the administration of adjuvant therapy, were fractionated using anion-exchange chromatography, to facilitate the detection of the low-abundant serum peptides. Selected fractions were subsequently analysed by surface-enhanced laser desorption/ionisation time-of-flight mass spectrometry (SELDI-TOF MS), and the resulting protein profiles were searched for prognostic markers by appropriate bioinformatics tools. RESULTS: Four peak clusters (i.e. m/z 3073, m/z 3274, m/z 4405 and m/z 7973) were found to bear significant prognostic value (P </= 0.01). The m/z 3274 candidate marker was structurally identified as inter-alpha-trypsin inhibitor heavy chain 4 fragment(658-688) in serum. Except for the m/z 7973 peak cluster, these peaks remained independently associated with recurrence-free survival upon multivariate Cox regression analysis, including clinical parameters of known prognostic value in this study population. CONCLUSION: Investigation of the postoperative serum proteome by, e.g., anion-exchange fractionation followed by SELDI-TOF MS analysis is promising for the detection of novel prognostic factors. However, regarding the rather limited study population, validation of these results by analysis of independent study populations is warranted to assess the true clinical applicability of discovered prognostic markers. In addition, structural identification of the other markers will aid in elucidation of their role in breast cancer prognosis, as well as enable development of absolute quantitative assays
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