Acoustic attenuation in glasses and its relation with the boson peak

A theory for the vibrational dynamics in disordered solids [W. Schirmacher, Europhys. Lett. {\bf 73}, 892 (2006)], based on the random spatial variation of the shear modulus, has been applied to determine the wavevector ($k$) dependence of the Brillouin peak position ($\Omega_k)$ and width ($\Gamma_k$), as well as the density of vibrational states ($g(\omega)$), in disordered systems. As a result, we give a firm theoretical ground to the ubiquitous $k^2$ dependence of $\Gamma_k$ observed in glasses. Moreover, we derive a quantitative relation between the excess of the density of states (the boson peak) and $\Gamma_k$, two quantities that were not considered related before. The successful comparison of this relation with the outcome of experiments and numerical simulations gives further support to the theory.Comment: To appear on PR

Euclidean random matrix theory: low-frequency non-analyticities and Rayleigh scattering

By calculating all terms of the high-density expansion of the euclidean random matrix theory (up to second-order in the inverse density) for the vibrational spectrum of a topologically disordered system we show that the low-frequency behavior of the self energy is given by $\Sigma(k,z)\propto k^2z^{d/2}$ and not $\Sigma(k,z)\propto k^2z^{(d-2)/2}$, as claimed previously. This implies the presence of Rayleigh scattering and long-time tails of the velocity autocorrelation function of the analogous diffusion problem of the form $Z(t)\propto t^{(d+2)/2}$.Comment: 27 page

Harmonic Vibrational Excitations in Disordered Solids and the "Boson Peak"

We consider a system of coupled classical harmonic oscillators with spatially fluctuating nearest-neighbor force constants on a simple cubic lattice. The model is solved both by numerically diagonalizing the Hamiltonian and by applying the single-bond coherent potential approximation. The results for the density of states $g(\omega)$ are in excellent agreement with each other. As the degree of disorder is increased the system becomes unstable due to the presence of negative force constants. If the system is near the borderline of stability a low-frequency peak appears in the reduced density of states $g(\omega)/\omega^2$ as a precursor of the instability. We argue that this peak is the analogon of the "boson peak", observed in structural glasses. By means of the level distance statistics we show that the peak is not associated with localized states

The evolution of vibrational excitations in glassy systems

The equations of the mode-coupling theory (MCT) for ideal liquid-glass transitions are used for a discussion of the evolution of the density-fluctuation spectra of glass-forming systems for frequencies within the dynamical window between the band of high-frequency motion and the band of low-frequency-structural-relaxation processes. It is shown that the strong interaction between density fluctuations with microscopic wave length and the arrested glass structure causes an anomalous-oscillation peak, which exhibits the properties of the so-called boson peak. It produces an elastic modulus which governs the hybridization of density fluctuations of mesoscopic wave length with the boson-peak oscillations. This leads to the existence of high-frequency sound with properties as found by X-ray-scattering spectroscopy of glasses and glassy liquids. The results of the theory are demonstrated for a model of the hard-sphere system. It is also derived that certain schematic MCT models, whose spectra for the stiff-glass states can be expressed by elementary formulas, provide reasonable approximations for the solutions of the general MCT equations.Comment: 50 pages, 17 postscript files including 18 figures, to be published in Phys. Rev.

Pancreatic metastasis from gastric carcinoma: a case report

BACKGROUND: The pancreas is a rare but occasionally favored target for metastasis. Metastatic lesions in the pancreas have been described for various primary cancers, such as carcinomas of the lung, the breast, renal cell carcinoma and sarcomas. CASE PRESENTATION: We report the case of a 60-year old female with a mass in the pancreatic head four years after partial gastrectomy for gastric adenocarcinoma. The patient underwent a pancreatoduodenectomy. Pathological examination revealed metastases of the primary gastric carcinoma within the pancreatic head and in regional lymph nodes. CONCLUSIONS: Pancreatic tumors in patients with a history of non-pancreatic malignancy should always be considered to be a putative metastatic lesion at an unusual site. If the pancreas can be identified as the only site of spread, radical resection may prolong survival

Scaling of phononic transport with connectivity in amorphous solids

The effect of coordination on transport is investigated theoretically using random networks of springs as model systems. An effective medium approximation is made to compute the density of states of the vibrational modes, their energy diffusivity (a spectral measure of transport) and their spatial correlations as the network coordination $z$ is varied. Critical behaviors are obtained as $z\to z_c$ where these networks lose rigidity. A sharp cross-over from a regime where modes are plane-wave-like toward a regime of extended but strongly-scattered modes occurs at some frequency $\omega^*\sim z-z_c$, which does not correspond to the Ioffe-Regel criterion. Above $\omega^*$ both the density of states and the diffusivity are nearly constant. These results agree remarkably with recent numerical observations of repulsive particles near the jamming threshold \cite{ning}. The analysis further predicts that the length scale characterizing the correlation of displacements of the scattered modes decays as $1/\sqrt{\omega}$ with frequency, whereas for $\omega<<\omega^*$ Rayleigh scattering is found with a scattering length $l_s\sim (z-z_c)^3/\omega^4$. It is argued that this description applies to silica glass where it compares well with thermal conductivity data, and to transverse ultrasound propagation in granular matter

Frustration and sound attenuation in structural glasses

Three classes of harmonic disorder systems (Lennard-Jones like glasses, percolators above threshold, and spring disordered lattices) have been numerically investigated in order to clarify the effect of different types of disorder on the mechanism of high frequency sound attenuation. We introduce the concept of frustration in structural glasses as a measure of the internal stress, and find a strong correlation between the degree of frustration and the exponent alpha that characterizes the momentum dependence of the sound attenuation $Gamma(Q)$$\simeq$$Q^\alpha$. In particular, alpha decreases from about d+1 in low-frustration systems (where d is the spectral dimension), to about 2 for high frustration systems like the realistic glasses examined.Comment: Revtex, 4 pages including 4 figure

E–N-cadherin heterodimers define novel adherens junctions connecting endoderm-derived cells

Contradicting the “cadherin switch” model, mixed E-cadherin–N-cadherin heterodimeric adherens junctions are prevalent in a variety of endodermal cells and endoderm-derived tumors

همانژیواندوتلیومای اپیتلیویید کبدی بدخیم اولیه، یک مرور جامع از متون تحقیقی با تأکید بر درمان جراحی

زمینه و هدف: همانژیواندوتلیـومای اپیتلیویید کبدی (HEH) بدخیم، یک تومـور عروقی بدخیـم نادر با علت ناشناخته و سیر طبیعی متغیر است. نویسندگان این مقاله، مـرور جامعی از متـون تحقیقی در مـورد HEH را با تمـرکز بر پیامدهای بالینی پس از راهبـردهای درمانی متفاوت، ارائه می‌دهند. مواد و روش‌ها: در این مـرور، تمامی مجمـوعه‌های منتشر شده در مورد بیماران مبتلا به HEH (تعداد 434 بیمـار) از نخستین توصیف این بیمـاران در سال 1984 تا مقالة حاضر مـورد تحلیل قـرار گرفت. پارامتـرهای مرور شده شامل: داده‌های جمعیت ـ شناختی، تظاهـرات بالینی، روش‌های درمانی و پیامـدهای بالینی بود. یافته‌ها: میانگین سنی بیماران مبتلا به HEH، 7/41 سال و نسبت مرد به زن، 2 به 3 بود. شایعترین تظاهـرات بالینی: درد ربع فـوقانی راست شکم، هپاتومگالی و کاهش وزن بود. اغلـب بیماران با تومور چند کانونی که هر دو لـوب را درگیـر کرده، مـراجعه کردند. شایعترین مناطق درگیری خارج کبدی در زمان تشخیص: ریه، صفاق، گـره‌های لنفـاوی و استخوان بود. شایعتـرین تدابیـر درمانی: پیـوند کبد (LTx)‌ (8/44% از بیمـاران)، پیگیـری بدون درمان (8/24% از بیماران)، شیمی درمانی یا پرتو درمانی (21% از بیماران)، و رزکسیـون کبد (LRx) (4/9% از بیمـاران) بود. میـزان بقـای یک و پنـج سالة پس از LTx به ترتیب 96% و 5/54%، پس از عـدم درمان به ترتیب 3/39% و 5/4% پس از شیمـی درمانی یا پرتودرمانی به ترتیب 3/73% و 30% و پس از LRx به ترتیب 100% و 75% بود. نتیجه‌گیـری: LRx درمان انتخـابی برای بیمـاران مبتلا به HEH قابل رزکسیـون است، با این وجـود، به دلیل چند مـرکزی بودن HEH کبـدی، LTx به عنوان درمـان انتخـابی پیشنهـاد شده است. علاوه بر این، LTx گزینة قابل قبـولی برای بیمارانی است که HEH با تظاهـرات خارج کبدی دارند. شاید بتوان بیماران کاملاً گزینش شده را تحت LTx از اهـداء کنندة زنده (با حفـظ منبع اهـداء) قـرار داد. نقش درمان‌های کمکی مختلف برای بیمارن مبتلا به HEH همچنان نامعلـوم است