1,042 research outputs found
On the Computation of 16-QAM and 64-QAM Performance in Rayleigh-Fading Channels
No full textSUMMARY Quadrature Amplitude Modulation (QAM) schemes are attractive in terms of bandwidth efficiency and offer a number of subchannels with different integrities via both Gaussian and Rayleigh-fading channels, Specifically, the 16-QAM phasor constellation has two, while the 64-QAM possesses three such subchannels, which become dramatically different via Rayleigh-fading channels. The analytically derived bit error rate (BER) formulae yield virtually identical curves with simulation results, exhibiting adequate BERs for the highest integrity subchannels of both 16-QAM and 64-QAM to be further reduced by forward error correction coding (FEC). However, the BERs of the lower integrity subchannels require fading compensation to reduce their values for FEC techniques to become effective. This property creates ground for a variety of carefully matched, embedded mobile transmission schemes of different complexities. The practical implementation of such an embedded scheme is demonstrated by a low-cost, low-complexity and low consumption 50 kBd mobile video telephone scheme offering adequate speech and image quality for channel SNRs in excess of about 20 dB via Rayleigh-fading channels. key words: QAM theory; modulation for microcellular fading channels
Cellular Communications Using Aerial Platforms
No full textThis paper is devoted to the study of cellular communications using aerial platforms (APs). A set of key equations is derived that quantify the coverage area on the ground as a function of AP elevation, the operation of the adaptive multibeam antenna on the AP, and the formulation of contiguous terrestrial cells and their shapes. Specifically, we consider the deployment of an AP to provide terrestrial mobile radio communications using the universal mobile telecommunication system operating in its wide-band code-division multiple-access mode. Calculations are made of the number of users versus Eb/No for different service rates. Multi-tiered cellular structures having cells of different size that are steerable with the offered teletraffic are examined. The array structure to achieve this is identified. The preliminary results shows that an AP at a height of 21 km covers an area of radius 517 km. Up to 21 users per cell with a service rate of 8 kb/s can be accommodated in the 2.2-GHz band. These services can be provided within an area of radius 70 km with transmitted powers of less than 1 W. High system capacity is proved to be possible by constructing cells of radius as small as 100 m using square planar arrays with dimensions of less than 12 m x 12 m. The AP system provides high capacity and Doppler frequency shifts that only originate from roving mobiles
Introducing Microcells into Macrocellular Networks: A Case Study
No full textAbstract?The performance in terms of signal-to-interference ratio (SIR), teletraffic, and spectral efficiency of a combined macrocellular and microcellular network is investigated when either both types of cells share the same channel set, or when the channel set is partitioned between the macrocells and the microcells. The analysis is for time-division multiple access (TDMA) with frequency hopping, power control, and discontinuous transmission, and the radio channel is composed of an inverse fourth-power path loss law with log-normal fading. We commence by introducing a single microcell into a hexagonal cluster of macrocells before considering clustered microcells. Both omni-directional and sectorized cells are examined. We find that high reuse factors are required when channel sharing is employed. When channel partitioning is used, no co-channel interference occurs between the microcells and the macrocells allowing them to be planned independently. The reuse factors in the microcells and macrocells therefore do not need to be increased beyond conventional values. The outcome is that by opting for channel partitioning, the improvement in spectral efficiency compared to channel sharing is two to three times greater. Index Terms?Co-channel interference, land mobile radio cel-lular systems, time division multiaccess
Interaction-Driven Giant Orbital Magnetic Moments in Carbon Nanotubes
No full textCarbon nanotubes continue to be model systems for studies of confinement and interactions. This is particularly true in the case of so-called "ultraclean" carbon nanotube devices offering the study of quantum dots with extremely low disorder. The quality of such systems, however, has increasingly revealed glaring discrepancies between experiment and theory. Here, we address the outstanding anomaly of exceptionally large orbital magnetic moments in carbon nanotube quantum dots. We perform low temperature magnetotransport measurements of the orbital magnetic moment and find it is up to 7 times larger than expected from the conventional semiclassical model. Moreover, the magnitude of the magnetic moment monotonically drops with the addition of each electron to the quantum dot directly contradicting the widely accepted shell filling picture of single-particle levels. We carry out quasiparticle calculations, both from first principles and within the effective-mass approximation, and find the giant magnetic moments can only be captured by considering a self-energy correction to the electronic band structure due to electron-electron interactions.QN/van der Zant LabQN/Steele La
Chronicles of Oklahoma
No full textArticle describes the journey of the E. M. DeBerry family from Texas to Old Greer County and their life on the frontier. Author Annie Laurie Steele includes an account by her aunt, Miss Rosabel DeBerry, about hunting, cooking, taking care of livestock, and housing visitors in their pioneer home
The effect of varying oven temperatures and residence times on thermal desorption of n-hexane and 1-hexene from diffusive organic vapor dosimeters
No full textDue to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Bibliography: leaves 64-67.Not availabl
Dental analysis of Classic period population variability in the Maya area
No full textIn this dissertation I examine population history and structure in the Maya area during
the Classic period (A.D. 250-900). Within the Maya area, archaeologists have identified
regional variation in material culture between archaeological zones. These cultural differences
may correspond to biological differences between Classic Maya populations. I test the
hypothesis that Classic Maya population structure followed an isolation by distance model. I
collected dental nonmetric and metric traits on 977 skeletons, from 18 Classic period sites,
representing seven different archaeological zones. I corrected the data for intraobserver error.
For the dental nonmetric data, I developed a Maya-specific trait dichotomization scheme and
controlled for sex bias. I tested the dental metric data for normality and age affects. I imputed
missing dental metric data for some traits and the remaining set of traits was Q-mode
transformed to control for allometric factors. I analyzed the dental nonmetric and metric datasets
with both univariate and multivariate tests. I found, with a log likelihood ratio, that 50% of the
nonmetric traits exhibited statistically significant differences between Maya sites. I performed a
Mean Measure of Divergence analysis of the dental nonmetric dataset and found that majority of
the resulting pairwise distance values were significant. Using cluster analysis and
multidimensional scaling, I found that the dental nonmetric data do not support an isolation by
distance organization of Classic Maya population structure. In the ANOVA and MANOVA
tests, I did not find major statistically significant differences in dental metrics between Maya
sites. Using principal components analysis, a Mahalanobis Distance test, and R matrix analysis,
I found a generally similar patterning of the dental metric data. The dental metric data to not
support an isolation by distance model for Classic Maya population structure. However, the
geographically outlying sites from Kaminaljuyu and the Pacific Coast repeatedly plotted as
biological outliers. R matrix analysis indicates that gene flow, not genetic drift, dominated
Classic Maya population structure. Based on the results of the dental nonmetric and metric
analyses, I reject the hypothesis that isolation by distance is a valid model for Classic Maya
population structure. From the multivariate analyses of the dental nonmetric and metric data, a
few notable observations are made. The major sites of Tikal and Calakmul both demonstrate
substantial intrasite biological heterogeneity, with some affinity to other sites but with little to
one another. Piedras Negras demonstrates some evidence for genetic isolation from the other
lowland Maya sites. In the Pasi��n Zone, Seibal and Altar de Sacrificios demonstrate some
affinity to one another, though Dos Pilas is an outlier. The R matrix analysis found evidence of
Classic period immigration into Seibal from outside the network of sites tested. The Belize Zone
exhibited substantial heterogeneity among its sites, with the site of Colha showing some affinity
to the Central Zone. Copan, despite being a geographic outlier, demonstrates genetic affinity
with the rest of the Maya area. Kaminaljuyu and the Pacific Coast were both found to be
outliers. These results indicate that dental nonmetric and metric data are a useful tool for
investigating ancient biological variability in the Maya area and contribute to our expanding
understanding of population history in that region
Nanoelectromechanical resonators from high-T <sub>c</sub> superconducting crystals of Bi <sub>2</sub> Sr <sub>2</sub> Ca <sub>1</sub> Cu <sub>2</sub> O<IMG ALIGN=MIDDLE ALT=-8+δ
No full text In this report, we present nanoelectromechanical resonators fabricated with thin exfoliated crystals of a high-T c cuprate superconductor Bi 2 Sr 2 Ca 1 Cu 2 O. The mechanical readout is performed by capacitively coupling their motion to a coplanar waveguide microwave cavity fabricated with a superconducting alloy of molybdenum-rhenium. We demonstrate mechanical frequency tunability with external dc-bias voltage, and quality factors up to ∼36 600. Our spectroscopic and time-domain measurements show that mechanical dissipation in these systems is limited by the contact resistance arising from resistive outer layers. The temperature dependence of dissipation indicates the presence of tunneling states, further suggesting that their intrinsic performance could be as good as other two-dimensional atomic crystals such as graphene. Accepted Author ManuscriptQN/Steele La
Flux-mediated optomechanics with a transmon qubit in the single-photon ultrastrong-coupling regime
No full textWe propose a scheme for controlling a radio-frequency mechanical resonator at the quantum level using a superconducting qubit. The mechanical part of the circuit consists of a suspended micrometer-long beam that is embedded in the loop of a superconducting quantum interference device (SQUID) and is connected in parallel to a transmon qubit. Using realistic parameters from recent experiments with similar devices, we show that this configuration can enable a tuneable optomechanical interaction in the single-photon ultrastrong-coupling regime, where the radiation-pressure coupling strength is larger than both the transmon decay rate and the mechanical frequency. We investigate the dynamics of the driven system for a range of coupling strengths and find an optimum regime for ground-state cooling, consistent with previous theoretical investigations considering linear cavities. Furthermore, we numerically demonstrate a protocol for generating hybrid discrete- and continuous-variable entanglement as well as mechanical Schrödinger cat states, which can be realized within the current state of the art. Our results demonstrate the possibility of controlling the mechanical motion of massive objects using superconducting qubits at the single-photon level and could enable applications in hybrid quantum technologies as well as fundamental tests of quantum mechanics.QN/Blanter GroupQN/Bauer GroupQN/Steele La
Nonlinear couplings for quantum control of superconducting qubits and electrical/mechanical resonators
No full textThis thesis explores nonlinear couplings in superconducting circuits with the purpose of achieving quantum control over the elementary excitations of light and motion. It consists mainly of three research themes. The first theme concerns the experimental realisation of a tuneable coupling scheme, giving rise to different interactions with adjustable ratios, between two transmon qubits. The tuneable capabilities of the device together with its versatile geometry and high coherence make it an interesting building block for analog quantum simulators of certain classes of complex problems. The second theme concerns two theoretical proposals for controlling mechanical resonators using transmon qubits. In the first part we analyse an electromechanical circuit architecture giving rise to tuneable three-body interactions between two qubits and a mechanical beam. Several protocols are performed numerically demonstrating ground-state cooling and the creation of mechanical quantum states, such as single-phonon and multi-phonon superposition states as well as qubit-phonon entanglement. Additionally, schemes for generating arbitrary quantum states are explored. The second part relies on the same concept for coupling a mechanical resonator to a transmon qubit and explores the qubit-resonator system in the ultrastrong coupling regime, where the optomechanical coupling approaches or even exceeds the mechanical frequency. We find that for certain coupling strengths ground-state cooling is possible and devise a protocol for generating macroscopic quantum superposition states, known as “Shrödinger cats”, on the mechanical resonator. Finally, the third research theme presented in the thesis concerns an experiment where a cold superconducting qubit is employed to readout and control a thermally populated radio-frequency resonator coupled via a strong dispersive coupling. By means of reservoir engineering, ground-state cooling as well as stabilisation of Fock states in the resonator are demonstrated reaching a new operating regime for circuit quantum electrodynamics.QN/Steele La
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