2,142 research outputs found
Anderson Transition in Disordered Graphene
We use the regularized kernel polynomial method (RKPM) to numerically study
the effect disorder on a single layer of graphene. This accurate numerical
method enables us to study very large lattices with millions of sites, and
hence is almost free of finite size errors. Within this approach, both weak and
strong disorder regimes are handled on the same footing. We study the
tight-binding model with on-site disorder, on the honeycomb lattice. We find
that in the weak disorder regime, the Dirac fermions remain extended and their
velocities decrease as the disorder strength is increased. However, if the
disorder is strong enough, there will be a {\em mobility edge} separating {\em
localized states around the Fermi point}, from the remaining extended states.
This is in contrast to the scaling theory of localization which predicts that
all states are localized in two-dimensions (2D).Comment: 4 page
Abolishing user fees for children and pregnant women trebled uptake of malaria-related interventions in Kangaba, Mali.
Malaria is the most common cause of morbidity and mortality in children under 5 in Mali. Health centres provide primary care, including malaria treatment, under a system of cost recovery. In 2005, Médecins sans Frontieres (MSF) started supporting health centres in Kangaba with the provision of rapid malaria diagnostic tests and artemisinin-based combination therapy. Initially MSF subsidized malaria tests and drugs to reduce the overall cost for patients. In a second phase, MSF abolished fees for all children under 5 irrespective of their illness and for pregnant women with fever. This second phase was associated with a trebling of both primary health care utilization and malaria treatment coverage for these groups. MSF's experience in Mali suggests that removing user fees for vulnerable groups significantly improves utilization and coverage of essential health services, including for malaria interventions. This effect is far more marked than simply subsidizing or providing malaria drugs and diagnostic tests free of charge. Following the free care strategy, utilization of services increased significantly and under-5 mortality was reduced. Fee removal also allowed for more efficient use of existing resources, reducing average cost per patient treated. These results are particularly relevant for the context of Mali and other countries with ambitious malaria treatment coverage objectives, in accordance with the United Nations Millennium Development Goals. This article questions the effectiveness of the current national policy, and the effectiveness of reducing the cost of drugs only (i.e. partial subsidies) or providing malaria tests and drugs free for under-5s, without abolishing other related fees. National and international budgets, in particular those that target health systems strengthening, could be used to complement existing subsidies and be directed towards effective abolition of user fees. This would contribute to increasing the impact of interventions on population health and, in turn, the effectiveness of aid
A programmable two-qubit quantum processor in silicon
With qubit measurement and control fidelities above the threshold of
fault-tolerance, much attention is moving towards the daunting task of scaling
up the number of physical qubits to the large numbers needed for fault tolerant
quantum computing. Here, quantum dot based spin qubits may offer significant
advantages due to their potential for high densities, all-electrical operation,
and integration onto an industrial platform. In this system, the
initialisation, readout, single- and two-qubit gates have been demonstrated in
various qubit representations. However, as seen with other small scale quantum
computer demonstrations, combining these elements leads to new challenges
involving qubit crosstalk, state leakage, calibration, and control hardware
which provide invaluable insight towards scaling up. Here we address these
challenges and demonstrate a programmable two-qubit quantum processor in
silicon by performing both the Deutsch-Josza and the Grover search algorithms.
In addition, we characterise the entanglement in our processor through quantum
state tomography of Bell states measuring state fidelities between 85-89% and
concurrences between 73-80%. These results pave the way for larger scale
quantum computers using spins confined to quantum dots
Flexible Lipid Bilayers in Implicit Solvent
A minimalist simulation model for lipid bilayers is presented. Each lipid is
represented by a flexible chain of beads in implicit solvent. The hydrophobic
effect is mimicked through an intermolecular pair potential localized at the
``water''/hydrocarbon tail interface. This potential guarantees realistic
interfacial tensions for lipids in a bilayer geometry. Lipids self assemble
into bilayer structures that display fluidity and elastic properties consistent
with experimental model membrane systems. Varying molecular flexibility allows
for tuning of elastic moduli and area/molecule over a range of values seen in
experimental systems.Comment: 5 pages, 5 figure
Efficient magneto-optical trapping of a metastable helium gas
This article presents a new experiment aiming at BEC of metastable helium
atoms. It describes the design of a high flux discharge source of atoms and a
robust laser system using a DBR diode coupled with a high power Yb doped fiber
amplifier for manipulating the beam of metastable atoms. The atoms are trapped
in a small quartz cell in an extreme high vacuum. The trapping design uses an
additional laser (repumper) and allows the capture of a large number of
metastable helium atoms (approximately ) in a geometry favorable for
loading a tight magnetostatic trap.Comment: 12 pages, 7 figures, Late
Impact of E-Bikes on Cycling in Hilly Areas: Participants’ Experience of Electrically-Assisted Cycling in a UK Study
Electrically-assisted cycling can make a major contribution to sustainable mobility. For some people, hills are a barrier for cycling. This paper focuses on how and why electrically-assisted bikes make a difference to cycling in hilly contexts, and can thus be an important element of sustainable mobility in hilly geographies. It makes a novel contribution in being able to draw on recorded sensor data of the actual use of assistance in relation to the specific geography of the route cycled (GPS data), and interview/survey material. It shows that e-bikes extend the range, nature and scope of journeys manageable by bike, and therefore the general viability of e-bikes as alternative to other modes. It highlights that the benefits of using e-bikes are often also psychological, since they can change the overall enjoyability of the cycling experience in hilly areas. Resulting policy recommendations, that could lead to significant CO2 savings through the uptake of e-cycling in hilly contexts, include ‘try before you buy’ schemes, training for e-bike users and investing in relevant cycling infrastructure
Impact of E-Bikes on Cycling in Hilly Areas: Participants’ Experience of Electrically-Assisted Cycling in a UK Study
Electrically-assisted cycling can make a major contribution to sustainable mobility. For some people, hills are a barrier for cycling. This paper focuses on how and why electrically-assisted bikes make a difference to cycling in hilly contexts, and can thus be an important element of sustainable mobility in hilly geographies. It makes a novel contribution in being able to draw on recorded sensor data of the actual use of assistance in relation to the specific geography of the route cycled (GPS data), and interview/survey material. It shows that e-bikes extend the range, nature and scope of journeys manageable by bike, and therefore the general viability of e-bikes as alternative to other modes. It highlights that the benefits of using e-bikes are often also psychological, since they can change the overall enjoyability of the cycling experience in hilly areas. Resulting policy recommendations, that could lead to significant CO2 savings through the uptake of e-cycling in hilly contexts, include ‘try before you buy’ schemes, training for e-bike users and investing in relevant cycling infrastructure
ANALISIS KAPASITAS PENAMPANG SUNGAI TINGKULU DI KECAMATAN TIKALA KOTA MANADO
Sungai Tingkulu merupakan salah satu sungai di Kota Manado yang pernah meluap dan membanjiri beberapa daerah yang dilewatinya yang mengakibatkan kerugian bagi warga yang tinggal disekitar sungai maupun pengguna jalan raya. Oleh karena itu dalam mengantisipasi banjir yang kemungkinan akan terjadi kelak, dibutuhkan data mengenai kapasitas penampang sungai Tingkulu.Analisis dilakukan dengan mencari frekuensi hujan dengan metode Log Pearson III. Data hujan diambil dari pos hujan Tikala-Sawangan. Data curah hujan yang digunakan adalah data curah hujan harian maksimum dari tahun 2008 s/d 2017. Setelah didapat besar hujan, pemodelan hujan aliran pada program komputer HEC-HMS akan menggunakan metode HSS Soil Conservation Services, dan untuk kehilangan air dengan SCS Curve Number (CN). Untuk aliran dasar (baseflow) akan menggunakan metode recession. Dilakukan kalibrasi parameter HSS SCS sebelum melakukan simulasi debit banjir dengan menggunakan program komputer HEC-HMS. Dalam kalibrasi ini, parameter yang akan dikalibrasi adalah lag time, curve number, recession constant, baseflow dan ratio to peak. Untuk batasan setiap parameter disesuaikan dengan nilai standar pada program komputer HEC-HMS. Hasil kalibrasi menunjukan nilai Nash Sutchliffe Efficiency yang baik yaitu 0,911. Kemudian dilakukan analisis debit banjir dengan parameter terkalibrasi menggunakan program komputer HEC-HMS. Setelah itu didapat debit puncak hasil simulasi setiap kala ulang dan kemudian dimasukkan dalam program komputer HEC-RAS untuk simulasi tinggi muka air pada penampang yang telah diukur. Hasil simulasi menunjukkan bahwa semua penampang sungai Tingkulu yang ditinjau, sudah tidak mampu menampung debit banjir yang terjadi untuk kala ulang 5 tahun, 10 tahun, 25 tahun, 50 tahun, dan 100 tahun. Kata kunci : Banjir, Kapasitas Penampang Sungai, Tinggi Muka Air, HEC-HMS, HEC-RAS
Phase diagram of the metal-insulator transition in 2D electronic systems
We investigated the interdependence of the effects of disorder and carrier
correlations on the metal-insulator transition in two-dimensional electronic
systems. We present a quantitative metal-insulator phase diagram. Depending on
the carrier density we find two different types of metal-insulator transition -
a continuous localization for rs=<8 and a discontinuous transition at higher
rs. The critical level of disorder at the transition decreases with decreasing
carrier density. At very low carrier densities we find that the system is
always insulating. The value of the conductivity at the transition is
consistent with recent experimental measurements. The self-consistent method
which we have developed includes the effects of both disorder and correlations
on the transition, using a density relaxation theory with the Coulomb
correlations determined from numerical simulation data.Comment: 4 pages, RevTeX + epsf, 5 figures. New comments on conducting phase
and on the conductivity. References updated and correcte
Excitation of the molecular gas in the nuclear region of M82
We present high resolution HIFI spectroscopy of the nucleus of the
archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4
fine-structure lines are detected. Besides showing the effects of the overall
velocity structure of the nuclear region, the line profiles also indicate the
presence of multiple components with different optical depths, temperatures and
densities in the observing beam. The data have been interpreted using a grid of
PDR models. It is found that the majority of the molecular gas is in low
density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and
a relatively low UV radiation field (GO = 10^2). The remaining gas is
predominantly found in clouds with higher densities (n=10^5 cm^-3) and
radiation fields (GO = 10^2.75), but somewhat lower column densities
(N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1%
relative surface filling) component, with an even higher density (n=10^6 cm^-3)
and UV field (GO = 10^3.25). These results show the strength of multi-component
modeling for the interpretation of the integrated properties of galaxies.Comment: Accepted for publication in A&A Letter
- …