282 research outputs found
High frequency Scanning Gate Microscopy and local memory effect of carbon nanotube transistors
We use impedance spectroscopy to measure the high frequency properties of
single-walled carbon nanotube field effect transistors (swCN-FETs).
Furthermore, we extend Scanning Gate Microscopy (SGM) to frequencies up to
15MHz, and use it to image changes in the impedance of swCN-FET circuits
induced by the SGM-tip gate. In contrast to earlier reports, the results of
both experiments are consistent with a simple RC parallel circuit model of the
swCN-FET, with a time constant of 0.3 ms. We also use the SGM tip to show the
local nature of the memory effect normally observed in swCN-FETs, implying that
nanotube-based memory cells can be miniaturized to dimensions of the order of
tens of nm.Comment: 7 pages, 3 figures, to appear in Nano Letter
PROFESSIONAL AND CORPORATE DYNAMICS OUTSIDE THE COMPANY: ROLES OF INTERNET FORUMS IN CHANGE APPROPRIATION
This paper analyzes the use of an internet forum by employees of a retail chain in France to exchange information and discuss about a major corporate change. We show how the forum takes on core functions being neglected by the company and how it contributes to the appropriation of change. Through detailed analysis of the posts, we identity the professional logic at work and link it to corporate dynamics. This helps explaining, among others, the homogeneity of the topics discussed, which directly deal with change issues, and the defusing of a massive rejection of change. The method used to analyze the posts (combining human and partially automatic processing) and the criteria used to identify professional dynamics also have a broader academic interest
Anomalous diffusion for neuronal growth on surfaces with controlled geometries
Geometrical cues are known to play a very important role in neuronal growth
and the formation of neuronal networks. Here, we present a detailed analysis of
axonal growth and dynamics for neuronal cells cultured on patterned
polydimethylsiloxane surfaces. We use fluorescence microscopy to image neurons,
quantify their dynamics, and demonstrate that the substrate geometrical
patterns cause strong directional alignment of axons. We quantify axonal growth
and report a general stochastic approach that quantitatively describes the
motion of growth cones. The growth cone dynamics is described by Langevin and
Fokker-Planck equations with both deterministic and stochastic contributions.
We show that the deterministic terms contain both the angular and speed
dependence of axonal growth, and that these two contributions can be separated.
Growth alignment is determined by surface geometry, and it is quantified by the
deterministic part of the Langevin equation. We combine experimental data with
theoretical analysis to measure the key parameters of the growth cone motion:
speed and angular distributions, correlation functions, diffusion coefficients,
characteristics speeds and damping coefficients. We demonstrate that axonal
dynamics displays a cross-over from Brownian motion (Ornstein-Uhlenbeck
process) at earlier times to anomalous dynamics (superdiffusion) at later
times. The superdiffusive regime is characterized by non-Gaussian speed
distributions and power law dependence of the axonal mean square length and the
velocity correlation functions. These results demonstrate the importance of
geometrical cues in guiding axonal growth, and could lead to new methods for
bioengineering novel substrates for controlling neuronal growth and
regeneration.Comment: 27 pages, 13 figures. arXiv admin note: substantial text overlap with
arXiv:1903.0133
Hashimoto thyroiditis is more frequent than expected when diagnosed by cytology which uncovers a pre-clinical state
<p>Abstract</p> <p>Background</p> <p>Our Thyroid-Multidisciplinary Clinic is a large referral site for thyroid diseases. Thyroid biopsies are mainly performed for thyroid cancer screening. Yet, Hashimoto thyroiditis (HT) is being too frequently diagnosed. The prevalence of HT is reported as 0.3-1.2% or twice the prevalence of type 1 diabetes. However, the prevalence of HT confirmed by cytology is still uncertain. To evaluate different aspects of thyroid physiopathology including prevalence of Hashimoto's, a database of clinical features, ultrasound images and cytology results of patients referred for FNA of thyroid nodules was prospectively developed.</p> <p>Methods</p> <p>We retrospectively studied 811 consecutive patients for whom ultrasound guided thyroid FNA biopsies were performed at our clinic over 2.5 year period (Mar/2006-Sep/2008).</p> <p>Results</p> <p>The analysis of our database revealed that from 761 patients, 102 (13.4%) had HT, from whom 56 (7.4%) were euthyroid or had sub-clinical (non-hypothyroid) disease, and 46 (6%) were clinically hypothyroid.</p> <p>Conclusions</p> <p>This is the first study to show such a high prevalence of HT diagnosed by ultrasound-guided FNA. More strikingly, the prevalence of euthyroid HT, appears to be >5% similar to that of type 2 diabetes. Based on our results, there might be a need to follow up on cytological Hashimoto's to monitor for thyroid failure, especially in high risk states, like pregnancy. The potential risk for thyroid cancer in patients with biopsy-proven inflammation of thyroid epithelium remains to be established prospectively. However, it may explain the increased risk for thyroid cancer observed in patients with elevated but within normal TSH.</p
Elasticity Maps of Living Neurons Measured by Combined Fluorescence and Atomic Force Microscopy
Detailed knowledge of mechanical parameters such as cell elasticity,
stiffness of the growth substrate, or traction stresses generated during axonal
extensions is essential for understanding the mechanisms that control neuronal
growth. Here we combine Atomic Force Microscopy based force spectroscopy with
Fluorescence Microscopy to produce systematic, high-resolution elasticity maps
for three different types of live neuronal cells: cortical (embryonic rat),
embryonic chick dorsal root ganglion, and P-19 (mouse embryonic carcinoma stem
cells) neurons. We measure how the stiffness of neurons changes both during
neurite outgrowth and upon disruption of microtubules of the cell. We find
reversible local stiffening of the cell during growth, and show that the
increase in local elastic modulus is primarily due to the formation of
microtubules. We also report that cortical and P-19 neurons have similar
elasticity maps, with elastic moduli in the range 0.1-2 kPa, with typical
average values of 0.4 kPa (P-19) and 0.2 kPa (cortical). In contrast, DRG
neurons are stiffer than P-19 and cortical cells, yielding elastic moduli in
the range 0.1-8 kPa, with typical average values of 0.9 kPa. Finally, we report
no measurable influence of substrate protein coating on cell body elasticity
for the three types of neurons
- …