355 research outputs found
Energy-Efficient Antenna Selection and Power Allocation for Large-Scale Multiple Antenna Systems with Hybrid Energy Supply
The combination of energy harvesting and large-scale multiple antenna
technologies provides a promising solution for improving the energy efficiency
(EE) by exploiting renewable energy sources and reducing the transmission power
per user and per antenna. However, the introduction of energy harvesting
capabilities into large-scale multiple antenna systems poses many new
challenges for energy-efficient system design due to the intermittent
characteristics of renewable energy sources and limited battery capacity.
Furthermore, the total manufacture cost and the sum power of a large number of
radio frequency (RF) chains can not be ignored, and it would be impractical to
use all the antennas for transmission. In this paper, we propose an
energy-efficient antenna selection and power allocation algorithm to maximize
the EE subject to the constraint of user's quality of service (QoS). An
iterative offline optimization algorithm is proposed to solve the non-convex EE
optimization problem by exploiting the properties of nonlinear fractional
programming. The relationships among maximum EE, selected antenna number,
battery capacity, and EE-SE tradeoff are analyzed and verified through computer
simulations.Comment: IEEE Globecom 2014 Selected Areas in Communications Symposium-Green
Communications and Computing Trac
GreenDelivery: Proactive Content Caching and Push with Energy-Harvesting-based Small Cells
The explosive growth of mobile multimedia traffic calls for scalable wireless
access with high quality of service and low energy cost. Motivated by the
emerging energy harvesting communications, and the trend of caching multimedia
contents at the access edge and user terminals, we propose a paradigm-shift
framework, namely GreenDelivery, enabling efficient content delivery with
energy harvesting based small cells. To resolve the two-dimensional randomness
of energy harvesting and content request arrivals, proactive caching and push
are jointly optimized, with respect to the content popularity distribution and
battery states. We thus develop a novel way of understanding the interplay
between content and energy over time and space. Case studies are provided to
show the substantial reduction of macro BS activities, and thus the related
energy consumption from the power grid is reduced. Research issues of the
proposed GreenDelivery framework are also discussed.Comment: 15 pages, 5 figures, accepted by IEEE Communications Magazin
Ordered Semiconducting Nitrogen-Graphene Alloys
The interaction between substitutional nitrogen atoms in graphene is studied
by performing first principles calculations. The nearest neighbor interaction
between nitrogen dopants is highly repulsive because of the strong
electrostatic repulsion between nitrogen atoms, which prevents the full phase
separation in nitrogen doped graphene. Interestingly, there are two relatively
stable nitrogen-nitrogen pairs due to the anisotropy charge redistribution
induced by nitrogen doping. We reveal two stable semiconducting ordered N doped
graphene structures C3N and C12N through the cluster expansion technique and
particle swarm optimization method. In particular, C12N has a direct band gap
of 0.98 eV. The heterojunctions between C12N and graphene nanoribbons might be
promising organic solar cells
Accelerated quantum control in a three-level system by jumping along the geodesics
In a solid-state spin system, we experimentally demonstrate a protocol for
quantum-state population transfer with an improved efficiency compared to
traditional stimulated Raman adiabatic passage (STIRAP). Using the ground-state
triplet of the nitrogen-vacancy center in diamond, we show that the required
evolution time for high-fidelity state transfer can be reduced by almost one
order of magnitude. Furthermore, we establish an improved robustness against
frequency detuning caused by magnetic noise as compared to STIRAP. These
results provide a powerful tool for coherent spin manipulation in the context
of quantum sensing and quantum computation.Comment: 8 pages, 6 figure
Structure-Property Relationship in Layered BaMn2Sb2 and Ba2Mn3Sb2O2
Layered transition-metal compounds have received great attention owing to
their novel physical properties. Here, we present the structural, electronic,
thermal, and magnetic properties of BaMn2Sb2 and Ba2Mn3Sb2O2 single crystals,
both with the layered structure analogous to high-temperature superconductors.
While the Mn moment in the MnSb4 tetrahedral environment forms G-type
antiferromagnetic (AFM) ordering in both BaMn2Sb2 (TN1~443 K) and Ba2Mn3Sb2O2
(TN1~314 K), a short-range AFM order is found in the intercalated MnO2 layer at
a much lower temperature (TN2~60 K) in Ba2Mn3Sb2O2. The directions of the
ordered moments in these two magnetic sub-lattices of Ba2Mn3Sb2O2 are
perpendicular to each other, even though the system is electrically conductive.
This indicates that the large magnetic moments in these compounds are highly
localized, leading to negligible coupling between MnSb4 and MnO2 layers in
Ba2Mn3Sb2O2. These findings provide an insight into the
structure-magnetism-based design principle for new superconductors.Comment: 15 pages, 4 figures. 2 table
Excitatory nucleo-olivary pathway shapes cerebellar outputs for motor control
The brain generates predictive motor commands to control the spatiotemporal precision of high-velocity movements. Yet, how the brain organizes automated internal feedback to coordinate the kinematics of such fast movements is unclear. Here we unveil a unique nucleo-olivary loop in the cerebellum and its involvement in coordinating high-velocity movements. Activating the excitatory nucleo-olivary pathway induces well-timed internal feedback complex spike signals in Purkinje cells to shape cerebellar outputs. Anatomical tracing reveals extensive axonal collaterals from the excitatory nucleo-olivary neurons to downstream motor regions, supporting integration of motor output and internal feedback signals within the cerebellum. This pathway directly drives saccades and head movements with a converging direction, while curtailing their amplitude and velocity via the powerful internal feedback mechanism. Our finding challenges the long-standing dogma that the cerebellum inhibits the inferior olivary pathway and provides a new circuit mechanism for the cerebellar control of high-velocity movements.</p
Whole brain radiotherapy plus simultaneous in-field boost with image guided intensity-modulated radiotherapy for brain metastases of non-small cell lung cancer
BACKGROUND: Whole brain radiotherapy (WBRT) plus sequential focal radiation boost is a commonly used therapeutic strategy for patients with brain metastases. However, recent reports on WBRT plus simultaneous in-field boost (SIB) also showed promising outcomes. The objective of present study is to retrospectively evaluate the efficacy and toxicities of WBRT plus SIB with image guided intensity-modulated radiotherapy (IG-IMRT) for inoperable brain metastases of NSCLC. METHODS: Twenty-nine NSCLC patients with 87 inoperable brain metastases were included in this retrospective study. All patients received WBRT at a dose of 40 Gy/20 f, and SIB boost with IG-IMRT at a dose of 20 Gy/5 f concurrent with WBRT in the fourth week. Prior to each fraction of IG-IMRT boost, on-line positioning verification and correction were used to ensure that the set-up errors were within 2 mm by cone beam computed tomography in all patients. RESULTS: The one-year intracranial control rate, local brain failure rate, and distant brain failure rate were 62.9%, 13.8%, and 19.2%, respectively. The two-year intracranial control rate, local brain failure rate, and distant brain failure rate were 42.5%, 30.9%, and 36.4%, respectively. Both median intracranial progression-free survival and median survival were 10 months. Six-month, one-year, and two-year survival rates were 65.5%, 41.4%, and 13.8%, corresponding to 62.1%, 41.4%, and 10.3% of intracranial progression-free survival rates. Patients with Score Index for Radiosurgery in Brain Metastases (SIR) >5, number of intracranial lesions <3, and history of EGFR-TKI treatment had better survival. Three lesions (3.45%) demonstrated radiation necrosis after radiotherapy. Grades 2 and 3 cognitive impairment with grade 2 radiation leukoencephalopathy were observed in 4 (13.8%) and 4 (13.8%) patients. No dosimetric parameters were found to be associated with these late toxicities. Patients received EGFR-TKI treatment had higher incidence of grades 2–3 cognitive impairment with grade 2 leukoencephalopathy. CONCLUSIONS: WBRT plus SIB with IG-IMRT is a tolerable and effective treatment for NSCLC patients with inoperable brain metastases. However, the results of present study need to be examined by the prospective investigations
- …