35,486 research outputs found
Improving Air Interface User Privacy in Mobile Telephony
Although the security properties of 3G and 4G mobile networks have
significantly improved by comparison with 2G (GSM), significant shortcomings
remain with respect to user privacy. A number of possible modifications to 2G,
3G and 4G protocols have been proposed designed to provide greater user
privacy; however, they all require significant modifications to existing
deployed infrastructures, which are almost certainly impractical to achieve in
practice. In this article we propose an approach which does not require any
changes to the existing deployed network infrastructures or mobile devices, but
offers improved user identity protection over the air interface. The proposed
scheme makes use of multiple IMSIs for an individual USIM to offer a degree of
pseudonymity for a user. The only changes required are to the operation of the
authentication centre in the home network and to the USIM, and the scheme could
be deployed immediately since it is completely transparent to the existing
mobile telephony infrastructure. We present two different approaches to the use
and management of multiple IMSIs
Imaging and quantum efficiency measurement of chromium emitters in diamond
We present direct imaging of the emission pattern of individual
chromium-based single photon emitters in diamond and measure their quantum
efficiency. By imaging the excited state transition dipole intensity
distribution in the back focal plane of high numerical aperture objective, we
determined that the emission dipole is oriented nearly orthogonal to the
diamond-air interface. Employing ion implantation techniques, the emitters were
engineered with various proximities from the diamond-air interface. By
comparing the decay rates from the single chromium emitters at different depths
in the diamond crystal, an average quantum efficiency of 28% was measured.Comment: 11 pages and 4 figure
Ions at the air-water interface: An end to one hundred year old mystery?
Availability of highly reactive halogen ions at the surface of aerosols has
tremendous implications for the atmospheric chemistry. Yet neither simulations,
experiments, nor existing theories are able to provide a fully consistent
description of the electrolyte-air interface. In this paper a new theory is
proposed which allows us to explicitly calculate the ionic density profiles,
the surface tension, and the electrostatic potential difference across the
solution-air interface. Predictions of the theory are compared to experiments
and are found to be in excellent agreement. The theory also sheds new light on
one of the oldest puzzles of physical chemistry -- the Hofmeister effect
Multi-service systems: an enabler of flexible 5G air-interface
Multi-service system is an enabler to flexibly support
diverse communication requirements for the next generation
wireless communications. In such a system, multiple types of
services co-exist in one baseband system with each service having
its optimal frame structure and low out of band emission (OoBE)
waveforms operating on the service frequency band to reduce the
inter-service-band-interference (ISvcBI). In this article, a
framework for multi-service system is established and the
challenges and possible solutions are studied. The multi-service
system implementation in both time and frequency domain is
discussed. Two representative subband filtered multicarrier
(SFMC) waveforms: filtered orthogonal frequency division
multiplexing (F-OFDM) and universal filtered multi-carrier
(UFMC) are considered in this article. Specifically, the design
methodology, criteria, orthogonality conditions and prospective
application scenarios in the context of 5G are discussed. We
consider both single-rate (SR) and multi-rate (MR) signal
processing methods. Compared with the SR system, the MR
system has significantly reduced computational complexity at the
expense of performance loss due to inter-subband-interference
(ISubBI) in MR systems. The ISvcBI and ISubBI in MR systems
are investigated with proposed low-complexity interference
cancelation algorithms to enable the multi-service operation in
low interference level conditions
Interfacial deflection and jetting of a paramagnetic particle-laden fluid: theory and experiment
We describe the results of experiments and mathematical analysis of the deformation of a free surface by an aggregate of magnetic particles. The system we study is differentiated from ferrofluid systems because it contains regions rich with magnetic material as well as regions of negligible magnetic content. In our experiments, the magnetic force from a spherical permanent magnet collects magnetic particles to a liquid–air interface, and deforms the free surface to form a hump. The hump is composed of magnetic and non-magnetic regions due to the particle collection. When the magnet distance falls below a threshold value, we observe the transition of the hump to a jet. The mathematical model we develop, which consists of a numerical solution and an asymptotic approximation, captures the shape of the liquid–air interface during the deformation stage and a scaling prediction for the critical magnet distance for the hump to become a jet
An ellipsometric study of protein adsorption at the saliva-air interface
At the liquid-air interface of human saliva a protein layer is adsorbed. From ellipsometric measurements it was found that the thickness of the surface layer ranged from 400 to 3600 Å and the amount of protein material adsorbed was 9–340 mg/m2. Based on the concentration of protein in the layer the samples could be classified into two groups: a low concentration (ca. 0.15 g/ml) and a high concentration (0.7–1.1 g/ml). In the low concentration group the surface layers appeared to be thin (500–600 Å) while those in the high concentration group appeared to be much thicker (1000–3500 Å). A correlation between the bulk pH and the thickness of the surface layer could be established
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