664 research outputs found
Pseudoparticle Multipole Method: A Simple Method to Implement High-Accuracy Treecode
In this letter we describe the pseudoparticle multipole method (P2M2), a new
method to express multipole expansion by a distribution of pseudoparticles. We
can use this distribution of particles to calculate high order terms in both
the Barnes-Hut treecode and FMM. The primary advantage of P2M2 is that it works
on GRAPE. GRAPE is a special-purpose hardware for the calculation of
gravitational force between particles. Although the treecode has been
implemented on GRAPE, we could handle terms only up to dipole, since GRAPE can
calculate forces from point-mass particles only. Thus the calculation cost
grows quickly when high accuracy is required. With P2M2, the multipole
expansion is expressed by particles, and thus GRAPE can calculate high order
terms. Using P2M2, we implemented an arbitrary-order treecode on GRAPE-4.
Timing result shows GRAPE-4 accelerates the calculation by a factor between 10
(for low accuracy) to 150 (for high accuracy). Even on general-purpose
programmable computers, our method offers the advantage that the mathematical
formulae and therefore the actual program is much simpler than that of the
direct implementation of multipole expansion.Comment: 6 pages, 4 figures, latex, submitted to ApJ Letter
PROGRAPE-1: A Programmable, Multi-Purpose Computer for Many-Body Simulations
We have developed PROGRAPE-1 (PROgrammable GRAPE-1), a programmable
multi-purpose computer for many-body simulations. The main difference between
PROGRAPE-1 and "traditional" GRAPE systems is that the former uses FPGA (Field
Programmable Gate Array) chips as the processing elements, while the latter
rely on the hardwired pipeline processor specialized to gravitational
interactions. Since the logic implemented in FPGA chips can be reconfigured, we
can use PROGRAPE-1 to calculate not only gravitational interactions but also
other forms of interactions such as van der Waals force, hydrodynamical
interactions in SPH calculation and so on. PROGRAPE-1 comprises two Altera
EPF10K100 FPGA chips, each of which contains nominally 100,000 gates. To
evaluate the programmability and performance of PROGRAPE-1, we implemented a
pipeline for gravitational interaction similar to that of GRAPE-3. One pipeline
fitted into a single FPGA chip, which operated at 16 MHz clock. Thus, for
gravitational interaction, PROGRAPE-1 provided the speed of 0.96
Gflops-equivalent. PROGRAPE will prove to be useful for wide-range of
particle-based simulations in which the calculation cost of interactions other
than gravity is high, such as the evaluation of SPH interactions.Comment: 20 pages with 9 figures; submitted to PAS
GRAPE-5: A Special-Purpose Computer for N-body Simulation
We have developed a special-purpose computer for gravitational many-body
simulations, GRAPE-5. GRAPE-5 is the successor of GRAPE-3. Both consist of
eight custom pipeline chips (G5 chip and GRAPE chip). The difference between
GRAPE-5 and GRAPE-3 are: (1) The G5 chip contains two pipelines operating at 80
MHz, while the GRAPE chip had one at 20 MHz. Thus, the calculation speed of the
G5 chip and that of GRAPE-5 board are 8 times faster than that of GRAPE chip
and GRAPE-3 board. (2) The GRAPE-5 board adopted PCI bus as the interface to
the host computer instead of VME of GRAPE-3, resulting in the communication
speed one order of magnitude faster. (3) In addition to the pure 1/r potential,
the G5 chip can calculate forces with arbitrary cutoff functions, so that it
can be applied to Ewald or P^3M methods. (4) The pairwise force calculated on
GRAPE-5 is about 10 times more accurate than that on GRAPE-3. On one GRAPE-5
board, one timestep of 128k-body simulation with direct summation algorithm
takes 14 seconds. With Barnes-Hut tree algorithm (theta = 0.75), one timestep
of 10^6-body simulation can be done in 16 seconds.Comment: 19 pages, 24 Postscript figures, 3 tables, Latex, submitted to
Publications of the Astronomical Society of Japa
GRAPE-6A: A single-card GRAPE-6 for parallel PC-GRAPE cluster system
In this paper, we describe the design and performance of GRAPE-6A, a
special-purpose computer for gravitational many-body simulations. It was
designed to be used with a PC cluster, in which each node has one GRAPE-6A.
Such configuration is particularly effective in running parallel tree
algorithm. Though the use of parallel tree algorithm was possible with the
original GRAPE-6 hardware, it was not very cost-effective since a single
GRAPE-6 board was still too fast and too expensive. Therefore, we designed
GRAPE-6A as a single PCI card to minimize the reproduction cost and optimize
the computing speed. The peak performance is 130 Gflops for one GRAPE-6A board
and 3.1 Tflops for our 24 node cluster. We describe the implementation of the
tree, TreePM and individual timestep algorithms on both a single GRAPE-6A
system and GRAPE-6A cluster. Using the tree algorithm on our 16-node GRAPE-6A
system, we can complete a collisionless simulation with 100 million particles
(8000 steps) within 10 days.Comment: submitted to PAS
Long-term maintenance of hemoglobin levels in hemodialysis patients treated with bi-weekly epoetin beta pegol switched from darbepoetin alfa: a single-center, 12-month observational study in Japan
Recent evidence on maintenance administration of epoetin beta pegol, a continuous erythropoiesis receptor activator (CERA), in dialysis patients shows the clinical benefit of bi-weekly administration (Q2W) in improving hematopoiesis and iron use efficiency. We undertook a single-center observational study of 33 Japanese maintenance dialysis patients, whose anemia had been kept stable through weekly administration (Q1W) of darbepoetin (DA), to evaluate the effectiveness of CERA Q2W switched from DA in maintaining hemoglobin (Hb) levels over a 12-month period. The target Hb level was 10.0–12.0 g/dL. Throughout the 12-month period, the mean Hb was stably maintained at 10.5–10.8 g/dL, 69.7–87.9% of the patients achieving the target Hb level. The mean CERA dose was within the range of 62.9–78.8 µg/2 weeks. The average CERA dose adjustment frequency after switching was low at 0.42–0.67 times/3 months. In both subgroups stratified by the DA dose prior to the switch, Hb levels were kept stable during CERA administration; however, in the low-dose group (10–20 µg/week of DA), the CERA and iron doses decreased over time, whereas in the high-dose group (30–60 µg/week of DA) they remained unchanged. CERA Q2W achieved long-term successful anemia management in Japanese maintenance dialysis patients after switching from DA Q1W. CERA dose was adjusted based on an overall consideration of past changes in Hb levels, erythropoiesis-stimulating agent and iron doses. Subgroup analysis showed the CERA dose in the low-dose group decreased continuously, due possibly to a long-term improvement in iron use efficiency
Structure of Dark Matter Halos From Hierarchical Clustering. III. Shallowing of The Inner Cusp
We investigate the structure of the dark matter halo formed in the cold dark
matter scenarios by N-body simulations with parallel treecode on GRAPE cluster
systems. We simulated 8 halos with the mass of to
in the SCDM and LCDM model using up to 30 million
particles. With the resolution of our simulations, the density profile is
reliable down to 0.2 percent of the virial radius. Our results show that the
slope of inner cusp within 1 percent virial radius is shallower than -1.5, and
the radius where the shallowing starts exhibits run-to-run variation, which
means the innermost profile is not universal.Comment: 26 pages, 16 fugures, submitted to Ap
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