3,216 research outputs found
On Polynomial Recursive Sequences
We study the expressive power of polynomial recursive sequences, a nonlinear extension of the well-known class of linear recursive sequences. These sequences arise naturally in the study of nonlinear extensions of weighted automata, where (non)expressiveness results translate to class separations. A typical example of a polynomial recursive sequence is b_n = n!. Our main result is that the sequence u_n = n? is not polynomial recursive
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Multireference Stochastic Coupled Cluster.
We describe a modification of the stochastic coupled cluster algorithm that
allows the use of multiple reference determinants. By considering the secondary
references as excitations of the primary reference and using them to change the
acceptance criteria for selection and spawning, we obtain a simple form of
stochastic multireference coupled cluster which preserves the appealing aspects
of the single reference approach. The method is able to successfully describe
strongly correlated molecular systems using few references and low cluster
truncation levels, showing promise as a tool to tackle strong correlation in
more general systems. Moreover, it allows simple and comprehensive control of
the included references and excitorsthereof, and this flexibility can be taken
advantage of to gain insight into some of the inner workings of established
electronic structure methods
Suppressing quasiparticle poisoning with a voltage-controlled filter
We study single-electron charging events in an Al/InAs nanowire hybrid system
with deliberately introduced gapless regions. The occupancy of a Coulomb island
is detected using a nearby radio-frequency quantum dot as a charge sensor. We
demonstrate that a 1 micron gapped segment of the wire can be used to
efficiently suppress single electron poisoning of the gapless region and
therefore protect the parity of the island while maintaining good electrical
contact with a normal lead. In the absence of protection by charging energy,
the 1e switching rate can be reduced below 200 per second. In the same
configuration, we observe strong quantum charge fluctuations due to exchange of
electron pairs between the island and the lead. The magnetic field dependence
of the poisoning rate yields a zero-field superconducting coherence length of ~
90 nm
Multireference Stochastic Coupled Cluster.
We describe a modification of the stochastic coupled cluster algorithm that allows the use of multiple reference determinants. By considering the secondary references as excitations of the primary reference and using them to change the acceptance criteria for selection and spawning, we obtain a simple form of stochastic multireference coupled cluster which preserves the appealing aspects of the single-reference approach. The method is able to successfully describe strongly correlated molecular systems using few references and low cluster truncation levels, showing promise as a tool to tackle strong correlation in more general systems. Moreover, it allows simple and comprehensive control of the included references and excitors thereof, and this flexibility can be taken advantage of to gain insight into some of the inner workings of established electronic structure methods
Diagnostic accuracy of urinary prostate protein glycosylation profiling in prostatitis diagnosis
Introduction: Although prostatitis is a common male urinary tract infection, clinical diagnosis of prostatitis is difficult. The developmental mechanism of prostatitis is not yet unraveled which led to the elaboration of various biomarkers. As changes in asparagine-linked-(N-)-glycosylation were observed between healthy volunteers (HV), patients with benign prostate hyperplasia and prostate cancer patients, a difference could exist in biochemical parameters and urinary N-glycosylation between HV and prostatitis patients. We therefore investigated if prostatic protein glycosylation could improve the diagnosis of prostatitis.
Materials and methods: Differences in serum and urine biochemical markers and in total urine N-glycosylation profile of prostatic proteins were determined between HV (N = 66) and prostatitis patients (N = 36). Additionally, diagnostic accuracy of significant biochemical markers and changes in N-glycosylation was assessed.
Results: Urinary white blood cell (WBC) count enabled discrimination of HV from prostatitis patients (P < 0.001). Urinary bacteria count allowed for discriminating prostatitis patients from HV (P < 0.001). Total amount of biantennary structures (urinary 2A/MA marker) was significantly lower in prostatitis patients compared to HV (P < 0.001). Combining the urinary 2A/MA marker and urinary WBC count resulted in an AUC of 0.79, 95% confidence interval (CI) = (0.70-0.89) which was significantly better than urinary WBC count (AUC = 0.70, 95% CI = [0.59-0.82], P = 0.042) as isolated test.
Conclusions: We have demonstrated the diagnostic value of urinary N-glycosylation profiling, which shows great potential as biomarker for prostatitis. Further research is required to unravel the developmental course of prostatic inflammation
Symmetric Operation of the Resonant Exchange Qubit
We operate a resonant exchange qubit in a highly symmetric triple-dot
configuration using IQ-modulated RF pulses. At the resulting three-dimensional
sweet spot the qubit splitting is an order of magnitude less sensitive to all
relevant control voltages, compared to the conventional operating point, but we
observe no significant improvement in the quality of Rabi oscillations. For
weak driving this is consistent with Overhauser field fluctuations modulating
the qubit splitting. For strong driving we infer that effective voltage noise
modulates the coupling strength between RF drive and the qubit, thereby
quickening Rabi decay. Application of CPMG dynamical decoupling sequences
consisting of up to n = 32 {\pi} pulses significantly prolongs qubit coherence,
leading to marginally longer dephasing times in the symmetric configuration.
This is consistent with dynamical decoupling from low frequency noise, but
quantitatively cannot be explained by effective gate voltage noise and
Overhauser field fluctuations alone. Our results inform recent strategies for
the utilization of partial sweet spots in the operation and long-distance
coupling of triple-dot qubits.Comment: 6 pages, 5 figure
Negative spin exchange in a multielectron quantum dot
By operating a one-electron quantum dot (fabricated between a multielectron
dot and a one-electron reference dot) as a spectroscopic probe, we study the
spin properties of a gate-controlled multielectron GaAs quantum dot at the
transition between odd and even occupation number. We observe that the
multielectron groundstate transitions from spin-1/2-like to singlet-like to
triplet-like as we increase the detuning towards the next higher charge state.
The sign reversal in the inferred exchange energy persists at zero magnetic
field, and the exchange strength is tunable by gate voltages and in-plane
magnetic fields. Complementing spin leakage spectroscopy data, the inspection
of coherent multielectron spin exchange oscillations provides further evidence
for the sign reversal and, inferentially, for the importance of non-trivial
multielectron spin exchange correlations.Comment: 8 pages, including 4 main figures and 2 supplementary figurure
Noise suppression using symmetric exchange gates in spin qubits
We demonstrate a substantial improvement in the spin-exchange gate using
symmetric control instead of conventional detuning in GaAs spin qubits, up to a
factor-of-six increase in the quality factor of the gate. For symmetric
operation, nanosecond voltage pulses are applied to the barrier that controls
the interdot potential between quantum dots, modulating the exchange
interaction while maintaining symmetry between the dots. Excellent agreement is
found with a model that separately includes electrical and nuclear noise
sources for both detuning and symmetric gating schemes. Unlike exchange control
via detuning, the decoherence of symmetric exchange rotations is dominated by
rotation-axis fluctuations due to nuclear field noise rather than direct
exchange noise.Comment: 5 pages main text (4 figures) plus 5 pages supplemental information
(3 figures
Spectrum of the Nuclear Environment for GaAs Spin Qubits
Using a singlet-triplet spin qubit as a sensitive spectrometer of the GaAs
nuclear spin bath, we demonstrate that the spectrum of Overhauser noise agrees
with a classical spin diffusion model over six orders of magnitude in
frequency, from 1 mHz to 1 kHz, is flat below 10 mHz, and falls as for
frequency Hz. Increasing the applied magnetic field from
0.1 T to 0.75 T suppresses electron-mediated spin diffusion, which decreases
spectral content in the region and lowers the saturation frequency,
each by an order of magnitude, consistent with a numerical model. Spectral
content at megahertz frequencies is accessed using dynamical decoupling, which
shows a crossover from the few-pulse regime ( -pulses),
where transverse Overhauser fluctuations dominate dephasing, to the many-pulse
regime ( -pulses), where longitudinal Overhauser
fluctuations with a spectrum dominate.Comment: 6 pages, 4 figures, 8 pages of supplementary material, 5
supplementary figure
Long-Term Changes in Aluminum Fractions of Drainage Waters in Two Forest Catchments with Contrasting Lithology
Aluminum (Al) chemistry was studied in soils and waters of two catchments covered by spruce (Picea abies) monocultures in the Czech Republic that represent geochemical end-members of terrestrial and aquatic sensitivity to acidic deposition. The acid-sensitive Lysina catchment, underlain by granite, was compared to the acid-resistant Pluhův Bor catchment on serpentine. Organically-bound Al was the largest pool of reactive soil Al at both sites. Very high median total Al (Alt) concentrations (40 μmol L−1) and inorganic monomeric Al (Ali) concentrations (27 μmol L−1) were observed in acidic (pH 4.0) stream water at Lysina in the 1990s and these concentrations decreased to 32 μmol L−1 (Alt) and 13 μmol L−1 (Ali) in the 2000s. The potentially toxic Ali fraction decreased in response to long-term decreases in acidic deposition, but Ali remained the largest fraction. However, the organic monomeric (Alo) and particulate (Alp) fractions increased in the 2000s at Lysina. In contrast to Lysina, marked increases of Alt concentrations in circum-neutral waters at Pluhův Bor were observed in the 2000s in comparison with the 1990s. These increases were entirely due to the Alp fraction, which increased more than 3-fold in stream water and up to 8-fold in soil water in the A horizon. Increase of Alp coincided with dissolved organic carbon (DOC) increases. Acidification recovery may have increased the content of colloidal Al though the coagulation of monomeric Al
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