492 research outputs found
Delay Optimal Secrecy in Two-Relay Network
We consider a two-relay network in which a source aims to communicate a
confidential message to a destination while keeping the message secret from the
relay nodes. In the first hop, the channels from the source to the relays are
assumed to be block-fading and the channel states change arbitrarily -possibly
non-stationary and non-ergodic- across blocks. When the relay feedback on the
states of the source-to-relay channels is available on the source with no
delay, we provide an encoding strategy to achieve the optimal delay. We next
consider the case in which there is one-block delayed relay feedback on the
states of the source-to-relay channels. We show that for a set of channel state
sequences, the optimal delay with one-block delayed feedback differs from the
optimal delay with no-delayed feedback at most one block
Estimating Central Bank Behavior in Emerging Markets: The Case of Turkey
Design of policy rules for an an emerging market central bank (EMCB) operating in an inflation-targeting framework presents additional challenges beyond those for describing the behavior of a central bank in a developed economy. Even though an inflation-targeting regime entails abolishing the exchange rate target in favor of an inflation target, it is more difficult for an EMBC to ignore movements in exchange rates given the relatively shallow depth of financial markets and the the high degree of dollarization. Additionally the EMCB may be forced to change the pursued exchange rate regime following a capital account reversal so that linear Taylor rules may be inadequate for describing EMCB reactions. We develop an empirical framework that addresses these issues and propose a new methodology to estimate unobserved variables such as expected inflation and potential output within the rule. Specifically, we employ a structural, nonlinear Kalman filter algorithm to estimate time-dependent parameters and unobserved variables, and we experiment with various exchange rate mechanisms that can be employed by an EMCB. This approach allows us to track any changes in EMCB behavior - including regime shifts - following a switch to inflation targeting. Using post-2001 data from Turkey, which is a fairly dollarized small open economy, we document that the Central Bank of Turkey has given relatively more importance to the inflation gap than to the output gap or to exchange rates, but not until some time after it had switched to an inflation-targeting framework.Dual Extended Kalman Filter, Taylor Rule, inflation targeting, emerging markets
To Obtain or not to Obtain CSI in the Presence of Hybrid Adversary
We consider the wiretap channel model under the presence of a hybrid, half
duplex adversary that is capable of either jamming or eavesdropping at a given
time. We analyzed the achievable rates under a variety of scenarios involving
different methods for obtaining transmitter CSI. Each method provides a
different grade of information, not only to the transmitter on the main
channel, but also to the adversary on all channels. Our analysis shows that
main CSI is more valuable for the adversary than the jamming CSI in both
delay-limited and ergodic scenarios. Similarly, in certain cases under the
ergodic scenario, interestingly, no CSI may lead to higher achievable secrecy
rates than with CSI.Comment: 8 pages, 3 figure
Modeling and forecasting car ownership based on socio-economic and demographic indicators in Turkey
Since car ownership is an important determinant to analyze car travel behavior especially in developing countries, this paper deals with modeling and forecasting car ownership in Turkey based on socio-economic and demographic indicators such as Gross Domestic Product(GDP) per capita, Gasoline Price (GP), car price and number of employees by using multiple nonlinear regression analysis. Although most of
the studies on this subject prefer using annual data, we use monthly data for the analysis of car ownership since all explanatory variables and exchange rates used for the modeling are unstable and vary even in a short period in developing countries such as Turkey. Thus, it may be
possible to reflect the effects of socio-economic and demographic indicators on car ownership more properly. During the modeling process, exponential and polynomial nonlinear regression models are set up and then tested to investigate their applicability for car ownership
forecasting. Based on results of the Kolmogorov-Smirnov test, the polynomial models has been selected to forecast car ownership for the year 2035. In order to reveal the possible different trends of the independent variables in future, car ownership is forecasted along the scenarios
which are related to the GDP per capita and GP. Results show that Turkey’s car ownership may vary between 230 and 325 per thousand capita in 2035 depending on economic achievements, global oil prices and national taxation policies. The lowest and the highest values of the car ownership may provide insight to car producers and transport planners in Turkey. Another significant result presented in this study is that
car ownership rate will be substantially lower in Turkey than that in the European Union countries despite it has an increasing trend in the past two decades
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Non-isothermal phase-field simulations of laser-written in-plane SiGe heterostructures for photonic applications
Advanced solid-state devices, including lasers and modulators, require semiconductor heterostructures for nanoscale engineering of the electronic bandgap and refractive index. However, existing epitaxial growth methods are limited to fabrication of vertical heterostructures grown layer by layer. Here, we report the use of finite-element-method-based phase-field modelling with thermocapillary convection to investigate laser inscription of in-plane heterostructures within silicon-germanium films. The modelling is supported by experimental work using epitaxially-grown Si0.5Ge0.5 layers. The phase-field simulations reveal that various in-plane heterostructures with single or periodic interfaces can be fabricated by controlling phase segregation through modulation of the scan speed, power, and beam position. Optical simulations are used to demonstrate the potential for two devices: graded-index waveguides with Ge-rich (>70%) cores, and waveguide Bragg gratings with nanoscale periods (100–500 nm). Periodic heterostructure formation via sub-millisecond modulation of the laser parameters opens a route for post-growth fabrication of in-plane quantum wells and superlattices in semiconductor alloy films
DeepCut: Object Segmentation from Bounding Box Annotations using Convolutional Neural Networks
In this paper, we propose DeepCut, a method to obtain pixelwise object
segmentations given an image dataset labelled with bounding box annotations. It
extends the approach of the well-known GrabCut method to include machine
learning by training a neural network classifier from bounding box annotations.
We formulate the problem as an energy minimisation problem over a
densely-connected conditional random field and iteratively update the training
targets to obtain pixelwise object segmentations. Additionally, we propose
variants of the DeepCut method and compare those to a naive approach to CNN
training under weak supervision. We test its applicability to solve brain and
lung segmentation problems on a challenging fetal magnetic resonance dataset
and obtain encouraging results in terms of accuracy
Surface wave control for large arrays of microwave kinetic inductance detectors
Large ultra-sensitive detector arrays are needed for present and future
observatories for far infra-red, submillimeter wave (THz), and millimeter wave
astronomy. With increasing array size, it is increasingly important to control
stray radiation inside the detector chips themselves, the surface wave. We
demonstrate this effect with focal plane arrays of 880 lens-antenna coupled
Microwave Kinetic Inductance Detectors (MKIDs). Presented here are near field
measurements of the MKID optical response versus the position on the array of a
reimaged optical source. We demonstrate that the optical response of a detector
in these arrays saturates off-pixel at the dB level compared to the
peak pixel response. The result is that the power detected from a point source
at the pixel position is almost identical to the stray response integrated over
the chip area. With such a contribution, it would be impossible to measure
extended sources, while the point source sensitivity is degraded due to an
increase of the stray loading. However, we show that by incorporating an
on-chip stray light absorber, the surface wave contribution is reduced by a
factor 10. With the on-chip stray light absorber the point source response
is close to simulations down to the dB level, the simulation based on
an ideal Gaussian illumination of the optics. In addition, as a crosscheck we
show that the extended source response of a single pixel in the array with the
absorbing grid is in agreement with the integral of the point source
measurements.Comment: accepted for publication in IEEE Transactions on Terahertz Science
and Technolog
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