257 research outputs found
Multi-valent Ion Mediated Polyelectrolyte Association and Structure
Polyelectrolytes are commonly used to chelate multi-valent ions in aqueous
solutions, playing a critical role in water softening and the prevention of
mineralization. At sufficient ionic strength, ion-mediated
polyelectrolyte--polyelectrolyte interactions can precipitate
polyelectrolyte--ion complexes, a phenomenon known as "like-charge attraction".
While the significant influence of small ions on polyelectrolyte solution phase
behavior is recognized, the precise molecular mechanisms driving the
counterintuitive phenomenon remain largely elusive. In this study, we employ
all-atom molecular dynamics simulations to investigate the molecular mechanism
of like-charge attraction between two poly(acrylic acid) (PAA) chains in
solution. We find that moderate quantities of Ca ions induce attraction
between PAA chains, facilitated by the formation of PAA--Ca--PAA bridges
and a significant increase in the coordination of Ca ions by the PAA
chains. At high Ca number densities, ion bridges are disfavored due to
electrostatic screening, yet the chains are still attracted to each other due
to solvent-mediated interactions between the chains and their chelated ions.
The insights gleaned from this study not only enrich our understanding of the
intricate mechanism of like-charge attraction between polyanions in solution
but also illuminate the influence of multi-valent ions on polyelectrolyte
interactions.Comment: 15 pages, 6 figure
Continuous Monitoring of Rabi Oscillations in a Josephson Flux Qubit
Under resonant irradiation, a quantum system can undergo coherent (Rabi)
oscillations in time. We report evidence for such oscillations in a
_continuously_ observed three-Josephson-junction flux qubit, coupled to a
high-quality tank circuit tuned to the Rabi frequency. In addition to
simplicity, this method of_Rabi spectroscopy_ enabled a long coherence time of
about 2.5 microseconds, corresponding to an effective qubit quality factor
\~7000.Comment: REVTeX4, 4pp., 4 EPS figure files. v3: changed title, fixed typos;
final, to appear in PR
Postoperative Pharmacologic Anticoagulation following Temporal Lobe Resection of a Gliosarcoma in a Hypercoagulable Patient
Gliosarcomas are a rare subtype of glioblastomas associated with high rates of malignancy-associated venous thromboembolism (VTE). VTE risk is further increased in hypercoagulable patients upon discontinuing pharmacologic anticoagulation for surgery. We present a 60-year old obese male with history of hypercoagulability on apixaban who developed extensive thrombosis following resection of a gliosarcoma. Prior to temporal lobe resection, apixaban was discontinued and an IVC filter placed. On postoperative day 4, imaging revealed thrombosis above the IVC filter extending to the bilateral common, internal and external iliac, and femoral veins, requiring immediate anticoagulation and suction thrombectomy. Clinicians must balance the risk of VTE and intracerebral hemorrhage following neurosurgical. While withholding pharmacologic VTE is standard, hypercoagulable patients may benefit from pharmacologic prophylaxis postoperatively. Patients with multiple risk factors including malignancies with high rates VTE, like gliosarcomas, medical and hematological conditions, including idiopathic erythrocytosis, and history of VTE may benefit from earlier pharmacologic prophylaxis
Evidence for entangled states of two coupled flux qubits
We have studied the low-frequency magnetic susceptibility of two inductively
coupled flux qubits using the impedance measurement technique (IMT), through
their influence on the resonant properties of a weakly coupled high-quality
tank circuit. In a single qubit, an IMT dip in the tank's current--voltage
phase angle at the level anticrossing yields the amplitude of coherent flux
tunneling. For two qubits, the difference (IMT deficit) between the sum of
single-qubit dips and the dip amplitude when both qubits are at degeneracy
shows that the system is in a mixture of entangled states (a necessary
condition for entanglement). The dependence on temperature and relative bias
between the qubits allows one to determine all the parameters of the effective
Hamiltonian and equilibrium density matrix, and confirms the formation of
entangled eigenstates.Comment: 4 pages, 4 figures, final versio
Interpretation of cone penetration test data in layered soils using cavity expansion analysis
Cavity expansion theory plays an important role in many geotechnical engineering problems, including the cone penetration test (CPT). One of the challenges of interpreting CPT data is the delineation of interfaces between soil layers and the identification of distinct thin layers, a process which relies on an in-depth understanding of the relationship between penetrometer readings and soil properties. In this paper, analytical cavity expansion solutions in two concentric regions of soil are applied to the interpretation of CPT data, with a specific focus on the layered effects during penetration. The solutions provide a large-strain analysis of cavity expansion in two concentric regions for dilatant elastic-perfectly plastic material. The analysis of CPT data in two-layered soils highlights the effect of respective soil properties (strength, stiffness) on CPT measurements within the influence zones around the two-soil interface. Results show good comparisons with numerical results and elastic solutions. A simple superposition method of the two-layered analytical approach is applied to the analysis of penetration in multilayered soils. A good comparison with field data and numerical results is obtained. It is illustrated that the proposed parameters effectively capture the influence of respective soil properties in the thin-layer analysis. It is also shown that results based on this analysis have better agreement with numerical results compared with elastic solutions
Josephson-phase qubit without tunneling
We show that a complete set of one-bit gates can be realized by coupling the
two logical states of a phase qubit to a third level (at higher energy) using
microwave pulses. Thus, one can achieve coherent control without invoking any
tunneling between the qubit levels. We propose two implementations, using
rf-SQUIDs and d-wave Josephson junctions.Comment: REVTeX4, 4pp., 6 EPS figure files; N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: gate universality fleshed out,
small fix in d-wave decoherence para, discussion expanded, two Refs. added.
v3: some more Refs., a molecular example, and a few minor fixes; final, to
appear in PRB Rapid
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