14,590 research outputs found
Fluctuations and scaling in creep deformation
The spatial fluctuations of deformation are studied in creep in the Andrade's
power-law and the logarithmic phases, using paper samples. Measurements by the
Digital Image Correlation technique show that the relative strength of the
strain rate fluctuations increases with time, in both creep regimes. In the
Andrade creep phase characterized by a power law decay of the strain rate
, with , the fluctuations obey
, with . The local
deformation follows a data collapse appropriate for an absorbing
state/depinning transition. Similar behavior is found in a crystal plasticity
model, with a jamming or yielding phase transition
Multiperiodicity, modulations and flip-flops in variable star light curves I. Carrier fit method
The light curves of variable stars are commonly described using simple
trigonometric models, that make use of the assumption that the model parameters
are constant in time. This assumption, however, is often violated, and
consequently, time series models with components that vary slowly in time are
of great interest. In this paper we introduce a class of data analysis and
visualization methods which can be applied in many different contexts of
variable star research, for example spotted stars, variables showing the
Blazhko effect, and the spin-down of rapid rotators. The methods proposed are
of explorative type, and can be of significant aid when performing a more
thorough data analysis and interpretation with a more conventional method.Our
methods are based on a straightforward decomposition of the input time series
into a fast "clocking" periodicity and smooth modulating curves. The fast
frequency, referred to as the carrier frequency, can be obtained from earlier
observations (for instance in the case of photometric data the period can be
obtained from independently measured radial velocities), postulated using some
simple physical principles (Keplerian rotation laws in accretion disks), or
estimated from the data as a certain mean frequency. The smooth modulating
curves are described by trigonometric polynomials or splines. The data
approximation procedures are based on standard computational packages
implementing simple or constrained least-squares fit-type algorithms.Comment: 14 pages, 23 figures, submitted to Astronomy and Astrophysic
Nongalvanic thermometry for ultracold two-dimensional electron domains
Measuring the temperature of a two-dimensional electron gas at temperatures
of a few mK is a challenging issue, which standard thermometry schemes may fail
to tackle. We propose and analyze a nongalvanic thermometer, based on a quantum
point contact and quantum dot, which delivers virtually no power to the
electron system to be measured.Comment: 5 pages, 3 figure
Electromagnetic multipole theory for optical nanomaterials
Optical properties of natural or designed materials are determined by the
electromagnetic multipole moments that light can excite in the constituent
particles. In this work we present an approach to calculate the multipole
excitations in arbitrary arrays of nanoscatterers in a dielectric host medium.
We introduce a simple and illustrative multipole decomposition of the electric
currents excited in the scatterers and link this decomposition to the classical
multipole expansion of the scattered field. In particular, we find that
completely different multipoles can produce identical scattered fields. The
presented multipole theory can be used as a basis for the design and
characterization of optical nanomaterials
A new governance approach for multi-firm projects: lessons from Olkiluoto 3 and Flamanville 3 nuclear power plant projects
We analyze governance in two contemporary nuclear power plant projects: Olkiluoto 3 (Finland) and Flamanville 3 (France). We suggest that in the governance of large multi-firm projects, any of the prevalent governance approaches that rely on market, hierarchy, or hybrid forms, is not adequate as such. This paper opens up avenues towards a novel theory of governance in large projects by adopting a project network view with multiple networked firms within a single project, and by simultaneously going beyond organizational forms that cut across the traditional firm–market dichotomy. Our analysis suggests four changes in the prevailing perspective towards the governance of large projects. First, there should be a shift from viewing multi-firm projects as hierarchical contract organizations to viewing them as supply networks characterized by a complex and networked organizational structure. Second, there should be a shift in the emphasis of the predominant modes of governance, market and hierarchy towards novel governance approaches that emphasize network-level mechanisms such as self-regulation within the project. Third, there should be a shift from viewing projects as temporary endeavors to viewing projects as short-term events or episodes embedded in the long-term sphere of shared history and expected future activities among the involved actors. Fourth, there should be a shift from the prevailing narrow view of a hierarchical project management system towards an open system view of managing in complex and challenging institutional environments
Charge sensitivity of the Inductive Single-Electron Transistor
We calculate the charge sensitivity of a recently demonstrated device where
the Josephson inductance of a single Cooper-pair transistor is measured. We
find that the intrinsic limit to detector performance is set by oscillator
quantum noise. Sensitivity better than e is
possible with a high -value , or using a SQUID amplifier. The
model is compared to experiment, where charge sensitivity e and bandwidth 100 MHz are achieved.Comment: 3 page
Cyclostationary shot noise in mesoscopic measurements
We discuss theoretically a setup where a time-dependent current consisting of
a DC bias and two sinusoidal harmonics is driven through a sample. If the
sample exhibits current-dependent shot noise, the down-converted noise power
spectrum varies depending on the local-oscillator phase of the mixer. The
theory of this phase-dependent noise is applied to discuss the measurement of
the radio-frequency single-electron transistor. We also show that this effect
can be used to measure the shot noise accurately even in nonlinear
high-impedance samples.Comment: 3 pages, 2 figure
Tunability of the optical absorption in small silver cluster-polymer hybrid systems
We have calculated the absorption characteristics of different hybrid systems
consisting of Ag, Ag2 or Ag3 atomic clusters and poly(methacrylic acid) (PMAA)
using the time-dependent density-functional theory. The polymer is found to
have an extensive structural-dependency on the spectral patterns of the hybrid
systems relative to the bare clusters. The absorption spectrum can be `tuned'
to the visible range for hybrid systems with an odd number of electrons per
silver cluster, whereas for hybrid systems comprising an even number of
electrons, the leading absorption edge can be shifted up to about 4.5 eV. The
results give theoretical support to the experimental observations on the
absorption in the visible range in metal cluster-polymer hybrid structures.Comment: Updated layout and minor changes in versions 2 and
Comment on: "Roughness of Interfacial Crack Fronts: Stress-Weighted Percolation in the Damage Zone"
This is a comment on J. Schmittbuhl, A. Hansen, and G. G. Batrouni, Phys.
Rev. Lett. 90, 045505 (2003). They offer a reply, in turn.Comment: 1 page, 1 figur
Shot Noise with Interaction Effects in Single Walled Carbon Nanotubes
We have measured shot noise in single walled carbon nanotubes (SWNT) with
good contacts at 4.2 K at low frequencies ( MHz). We find a strong
modulation of shot noise over the Fabry-Perot pattern; in terms of differential
Fano factor the variation ranges over 0.4 - 1.2. The shot noise variation, in
combination with differential conductance, is analyzed using two
(spin-degenerate) modes with different, energy-dependent transmission
coefficients. No power law dependence of shot noise, as expected for Luttinger
liquids, was found in our measurements.Comment: 5 pages, 4 figure
- …