12,982 research outputs found
On-stack replacement, distilled
On-stack replacement (OSR) is essential technology for adaptive optimization, allowing changes to code actively executing in a managed runtime. The engineering aspects of OSR are well-known among VM architects, with several implementations available to date. However, OSR is yet to be explored as a general means to transfer execution between related program versions, which can pave the road to unprecedented applications that stretch beyond VMs. We aim at filling this gap with a constructive and provably correct OSR framework, allowing a class of general-purpose transformation functions to yield a special-purpose replacement. We describe and evaluate an implementation of our technique in LLVM. As a novel application of OSR, we present a feasibility study on debugging of optimized code, showing how our techniques can be used to fix variables holding incorrect values at breakpoints due to optimizations
Nanostructures from self-assembling triazine tertiary amine N-oxide amphiphiles
A new set of amphiphilic tertiary amine N-oxides has been prepared and their self-assembly properties observed in aqueous solution by tensiometry, dynamic and static light scattering. X-ray crystallographic analysis of parent amines and sulfoxide congeners indicates the formation of hydrogen bonded dimers as the primary assembly unit for formation of vesicles in preference to the compact micelles typical of lauryl dimethylamine N-oxide (LDAO). 6-Benzyloxy-N,N'-bis(5-diethylaminopentylamine oxide)[1,3,5]triazine-2,4-diamine forms a 1 μm vesicle observed to entrap fluorescein. The [1,3,5]triazine core thus allows variation of the new self-assembled structures from nano- to micrometre length scales
Spectroscopic characterization of the oxo-transfer reaction from a bis(µ-oxo)dicopper(III) complex to triphenylphosphine
The oxygen-atom transfer reaction from the bis(µ-oxo)dicopper(III) complex [CuIII2(µ-O)2(L)2]2+1, where L =N,N,N,N -tetraethylethylenediamine, to PPh3 has been studied by UV-vis, EPR, 1H NMR and Cu K-edge X-ray absorption spectroscopy in parallel at low temperatures (193 K) and above. Under aerobic conditions (excess dioxygen), 1 reacted with PPh3, giving OPPh3 and a diamagnetic species that has been assigned to an oxo-bridged dicopper(II) complex on the basis of EPR and Cu K-edge X-ray absorption spectroscopic data. Isotope-labeling experiments (18O2) established that the oxygen atom incorporated into the triphenylphosphine oxide came from both complex 1 and exogenous dioxygen. Detailed kinetic studies revealed that the process is a third-order reaction; the rate law is first order in both complex 1 and triphenylphosphine, as well as in dioxygen. At temperatures above 233 K, reaction of 1 with PPh3 was accompanied by ligand degradation, leading to oxidative N-dealkylation of one of the ethyl groups. By contrast, when the reaction was performed in the absence of excess dioxygen, negligible substrate (PPh3) oxidation was observed. Instead, highly symmetrical copper complexes with a characteristic isotropic EPR signal at g= 2.11 were formed. These results are discussed in terms of parallel reaction channels that are activated under various conditions of temperature and dioxygen
Evaluation of the economic and environmental performance of low-temperature heat to power conversion using a reverse electrodialysis - Multi-effect distillation system
In the examined heat engine, reverse electrodialysis (RED) is used to generate electricity from the salinity difference between two artificial solutions. The salinity gradient is restored through a multi-effect distillation system (MED) powered by low-temperature waste heat at 100 ◦C. The current work presents the first comprehensive economic and environmental analysis of this advanced concept, when varying the number of MED effects, the system sizing, the salt of the solutions, and other key parameters. The levelized cost of electricity (LCOE) has been calculated, showing that competitive solutions can be reached only when the system is at least medium to large scale. The lowest LCOE, at about 0.03 €/kWh, is achieved using potassium acetate salt and six MED effects while reheating the solutions. A similar analysis has been conducted when using the system in energy storage mode, where the two regenerated solutions are stored in reservoir tanks and the RED is operating for a few hours per day, supplying valuable peak power, resulting in a LCOE just below 0.10 €/kWh. A life-cycle assessment has been also carried out, showing that the case with the lowest environmental impact is the same as the one with the most attractive economic performance. Results indicate that the material manufacturing has the main impact; primarily the metallic parts of the MED. Overall, this study highlights the development efforts required in terms of both membrane performance and cost reduction, in order to make this technology cost effective in the future
Layered architecture for quantum computing
We develop a layered quantum computer architecture, which is a systematic
framework for tackling the individual challenges of developing a quantum
computer while constructing a cohesive device design. We discuss many of the
prominent techniques for implementing circuit-model quantum computing and
introduce several new methods, with an emphasis on employing surface code
quantum error correction. In doing so, we propose a new quantum computer
architecture based on optical control of quantum dots. The timescales of
physical hardware operations and logical, error-corrected quantum gates differ
by several orders of magnitude. By dividing functionality into layers, we can
design and analyze subsystems independently, demonstrating the value of our
layered architectural approach. Using this concrete hardware platform, we
provide resource analysis for executing fault-tolerant quantum algorithms for
integer factoring and quantum simulation, finding that the quantum dot
architecture we study could solve such problems on the timescale of days.Comment: 27 pages, 20 figure
Quantum identification system
A secure quantum identification system combining a classical identification
procedure and quantum key distribution is proposed. Each identification
sequence is always used just once and new sequences are ``refuelled'' from a
shared provably secret key transferred through the quantum channel. Two
identification protocols are devised. The first protocol can be applied when
legitimate users have an unjammable public channel at their disposal. The
deception probability is derived for the case of a noisy quantum channel. The
second protocol employs unconditionally secure authentication of information
sent over the public channel, and thus it can be applied even in the case when
an adversary is allowed to modify public communications. An experimental
realization of a quantum identification system is described.Comment: RevTeX, 4 postscript figures, 9 pages, submitted to Physical Review
Overlimiting Current and Shock Electrodialysis in Porous Media
Most electrochemical processes, such as electrodialysis, are limited by
diffusion, but in porous media, surface conduction and electro-osmotic flow
also contribute to ionic fluxes. In this paper, we report experimental evidence
for surface-driven over-limiting current (faster than diffusion) and
deionization shocks (propagating salt removal) in a porous medium. The
apparatus consists of a silica glass frit (1 mm thick with 500 nm mean pore
size) in an aqueous electrolyte (CuSO or AgNO) passing ionic current
from a reservoir to a cation-selective membrane (Nafion). The current-voltage
relation of the whole system is consistent with a proposed theory based on the
electro-osmotic flow mechanism over a broad range of reservoir salt
concentrations (0.1 mM - 1.0 M), after accounting for (Cu) electrode
polarization and pH-regulated silica charge. Above the limiting current,
deionized water ( ) can be continuously extracted from the
frit, which implies the existence of a stable shock propagating against the
flow, bordering a depleted region that extends more than 0.5mm across the
outlet. The results suggest the feasibility of "shock electrodialysis" as a new
approach to water desalination and other electrochemical separations.Comment: 39 pages, 9 fig
Toxic Hazards Research Unit annual technical report, 1969 Final report, Jun. 1968 - May 1969
Apollo materials toxicity screening tests and effects of ethylene glycol, monomethylhydrazine, NF3, OF2, and ClF
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