Mechanical Properties of Growing Melanocytic Nevi and the Progression to Melanoma

Melanocytic nevi are benign proliferations that sometimes turn into malignant melanoma in a way that is still unclear from the biochemical and genetic point of view. Diagnostic and prognostic tools are then mostly based on dermoscopic examination and morphological analysis of histological tissues. To investigate the role of mechanics and geometry in the morpholgical dynamics of melanocytic nevi, we study a computation model for cell proliferation in a layered non-linear elastic tissue. Numerical simulations suggest that the morphology of the nevus is correlated to the initial location of the proliferating cell starting the growth process and to the mechanical properties of the tissue. Our results also support that melanocytes are subject to compressive stresses that fluctuate widely in the nevus and depend on the growth stage. Numerical simulations of cells in the epidermis releasing matrix metalloproteinases display an accelerated invasion of the dermis by destroying the basal membrane. Moreover, we suggest experimentally that osmotic stress and collagen inhibit growth in primary melanoma cells while the effect is much weaker in metastatic cells. Knowing that morphological features of nevi might also reflect geometry and mechanics rather than malignancy could be relevant for diagnostic purpose

Volume changes during active shape fluctuations in cells

Cells modify their volume in response to changes in osmotic pressure but it is usually assumed that other active shape variations do not involve significant volume fluctuations. Here we report experiments demonstrating that water transport in and out of the cell is needed for the formation of blebs, commonly observed protrusions in the plasma membrane driven by cortex contraction. We develop and simulate a model of fluid mediated membrane-cortex deformations and show that a permeable membrane is necessary for bleb formation which is otherwise impaired. Taken together our experimental and theoretical results emphasize the subtle balance between hydrodynamics and elasticity in actively driven cell morphological changes.Comment: Phys. Rev. Lett. in press. 13 pages 4 figures, 9 supplementary figure

Protein-driven lipid domain nucleation in biological membranes

Lipid rafts are heterogeneous dynamic lipid domains of the cell membranes that are involved in several biological processes, such as protein and lipid specific transport and signaling. Our understanding of lipid raft formation is still limited due to the transient and elusive nature of these domains in vivo, in contrast with the stable phase-separated domains observed in artificial membranes. Inspired by experimental findings highlighting the relevance of transmembrane proteins for lipid rafts, we investigate lipid domain nucleation by coarse-grained molecular dynamics and Ising-model simulations. We find that the presence of a transmembrane protein can trigger lipid domain nucleation in a flat membrane from an otherwise mixed lipid phase. Furthermore, we study the role of the lipid domain in the diffusion of the protein showing that its mobility is hindered by the presence of the raft. The results of our coarse-grained molecular-dynamics and Ising-model simulations thus coherently support the important role played by transmembrane proteins in lipid domain formation and stability

Acoustic emission (AE) as a diagnostic tool in geophysics

Acoustic Emissions (AE) are effective for monitoring ground deformation and temporal variation of its porosity. AE are complementary to seismic information, related to the same area, though AE and earthquakes focus on observational evidence concerned with substantially different space- and time-scales. AE information is pertinent (i) either for geodynamically stable areas, where it probes the diurnal thermal and/or tidal deformation, (ii) or for seismic areas where it provides some as yet unexploited precursors, (iii) or for volcanic areas, where it appears capable of recognising precursors originated by some hot fluid that penetrates by diffusion into rock pores, from those associated with eventual plutonic magma intrusions, (iv) and also for monitoring periods of time during which a volcano is «inflated» by underground hot fluids compared to others during which it «deflates». Upon direct comparison between 6 data sets concerned with different physical settings, it seems to be possible (fig. 3 and table II] to distinguish a few significantly different behaviours associated either (i) with a mere compression (such as it occurs for Stromboli, Vesuvius, and a sample compressed in the laboratory), or (ii) with a slip strain, such as it typically occurs in association with faulting or with diurnal thermal rock deformation

OKULASI TANAMAN DURIAN “Durio zibethinus Murr.” DENGAN ASAL TUNAS BATANG ATAS DAN CARA PEMOTONGAN BATANG BAWAH

Durian memiliki prospek ekonomi yang bagus sebab pemasaran meningkat dari tahun ke tahun, akan tetapi ketersediaan benih bermutu masih terbatas. Penyediaan benih bermutu perlu dilakukan dengan cara gabungan (vegetatif dan generatif) salah satunya adalah okulasi. Pertumbuhan okulasi dipengaruhi oleh asal tunas yang menunjukkan tingkat ketuaan batang dan pemotongan batang bawah yang akan menekan pertumbuhan tunas lateral, sehingga perlu dilakukan pemotongan dengan ukuran yang tepat. Tujuan dari penelitian ini untuk mempelajari asal tunas dan mendapatkan panjang pemotongan batang bawah yang tepat untuk mempercepat pertumbuhan tunas okulasi serta mendapatkan kesesuaian antara asal tunas batang atas dengan pemotongan batang bawah terhadap pertumbuhan tunas okulasi. Penelitian dilaksanakan bulan Januari sampai Mei 2011 berdasarkan percobaan faktorial dengan rancangan acak lengkap, diulang empat kali, yang terdiri atas dua faktor yaitu asal entres (ujung, tengah, pangkal) dan pemotongan batang bawah (dipotong ½ batang, 10 cm dari ujung, 15 cm dan 5 cm di atas okulasi), sehingga diperoleh 12 kombinasi perlakuan. Variabel pengamatan meliputi jumlah keberhasilan okulasi, saat pecah mata entres, saat kemunculan daun pertama, tinggi tunas okulasi, jumlah daun, keberhasilan okulasi tumbuh. Hasil penelitian menunjukkan entres ujung diawal pertumbuhan tumbuh lebih cepat dibandingkan yang lain meskipun selanjutnya entres tengah memberikan pertumbuhan yang lebih baik. Panjang pemotongan batang bawah yang tepat adalah 10 cm dari ujung batang bawah. Secara keseluruhan perbanyakan vegetatif dengan okulasi menggunakan entres tengah dan pemotongan batang bawah 10 cm dari ujung menghasilkan pertumbuhan yang lebih baik. Unrestrict PDF - Trial Edition Website

Langevin formulation for single-file diffusion

We introduce a stochastic equation for the microscopic motion of a tagged particle in the single file model. This equation provides a compact representation of several of the system's properties such as Fluctuation-Dissipation and Linear Response relations, achieved by means of a diffusion noise approach. Most important, the proposed Langevin Equation reproduces quantitatively the \emph{three} temporal regimes and the corresponding time scales: ballistic, diffusive and subdiffusive.Comment: 9 pages, 5 figures, 1 table, to appear in Physical Review

Fingered growth in channel geometry: A Loewner equation approach

A simple model of Laplacian growth is considered, in which the growth takes place only at the tips of long, thin fingers. In a recent paper, Carleson and Makarov used the deterministic Loewner equation to describe the evolution of such a system. We extend their approach to a channel geometry and show that the presence of the side walls has a significant influence on the evolution of the fingers and the dynamics of the screening process, in which longer fingers suppress the growth of the shorter ones

Acoustic Emission (AE) as a diagnostic tool in geophysics

Acoustic Emissions (AE) are effective for monitoring ground deformation and temporal variation of its porosity. AE are complementary to seismic information, related to the same area, though AE and earthquakes focus on observational evidence concerned with substantially different space- and time-scales. AE information is pertinent (i) either for geodynamically stable areas, where it probes the diurnal thermal and/or tidal deformation, (ii) or for seismic areas where it provides some as yet unexploited precursors, (iii) or for volcanic areas, where it appears capable of recognising precursors originated by some hot fluid that penetrates by diffusion into rock pores, from those associated with eventual plutonic magma intrusions, (iv) and also for monitoring periods of time during which a volcano is «inflated» by underground hot fluids compared to others during which it «deflates». Upon direct comparison between 6 data sets concerned with different physical settings, it seems to be possible (fig. 3 and table II] to distinguish a few significantly different behaviours associated either (i) with a mere compression (such as it occurs for Stromboli, Vesuvius, and a sample compressed in the laboratory), or (ii) with a slip strain, such as it typically occurs in association with faulting or with diurnal thermal rock deformation

Fluctuations in Protein Aggregation: Design of Preclinical Screening for Early Diagnosis of Neurodegenerative Disease

Autocatalytic fibril nucleation has recently been proposed to be a determining factor for the spread of neurodegenerative diseases, but the same process could also be exploited to amplify minute quantities of protein aggregates in a diagnostic context. Recent advances in microfluidic technology allow the analysis of protein aggregation in micron-scale samples, potentially enabling such diagnostic approaches, but the theoretical foundations for the analysis and interpretation of such data are, so far, lacking. Here, we study computationally the onset of protein aggregation in small volumes and show that the process is ruled by intrinsic fluctuations whose volume-dependent distribution we also estimate theoretically. Based on these results, we develop a strategy to quantify in silico the statistical errors associated with the detection of aggregate-containing samples. Our work explores a different perspective on the forecasting of protein aggregation in asymptomatic subjects