546 research outputs found
Nonprice Barriers to Ambulatory Care After an Emergency Department Visit
Study objective: Availability of timely follow-up care is essential in emergency medicine. We describe nonprice barriers to care experienced by callers reporting to be emergency department (ED) patients in need of follow-up care.
Methods: This was a secondary analysis of data collected during a survey of ambulatory clinics in 9 US cities. Research assistants called a random sample of 603 ambulatory clinics, generated from actual ED referral lists. Callers identified themselves as new patients referred by the local ED. Outcome measures were the percentage of callers experiencing failed appointment attempts for a variety of reasons and inconvenience factors associated with the appointment process: number and amount of time spent on hold, voicemail, repeated calls, and total telephone time.
Results: Only 242 (23%) of 1065 total calls resulted in an appointment within one week, for an ultimate caller success rate of 40% (242/603 pseudopatient scenarios). Independent of insurance status, 43% of 603 initial calls to ED referral numbers were unsuccessful: 27% of initial call failures were due to clinic closures, busy signals, voicemail, or personnel too busy to take the call; 6% wrong numbers; 4% disconnected or extended holds; and 6% out of practice scope. If they reached clinic personnel, 55% of callers were placed on hold; average hold time was 2.43 minutes (median 1.35 minutes). Answering system time averaged 1.17 minutes (median 0.68 minutes; range 0.02 to 13.90 minutes). On average, it required 1.7 calls to reach appointment staff and 8% of clinic contacts required 4 or more attempts. Total telephone time averaged 11.1 minutes for successful appointments.
Conclusion: There are important nonprice barriers to obtaining follow-up appointments for urgent conditions, independent of insurance status
analytical solutions for spectral patterns and their field dependence
We have obtained analytical solutions for Para-Hydrogen Induced Polarization
(PHIP) for several types of coupled spin systems, namely, for AB-, ABX-,
AA´A´´- and A2B-systems. Scalar spin-spin interactions were considered the
factor, that determines the PHIP spectral pattern; it is the variation of the
spin coupling regime (from strong coupling at low field to weak coupling at
high field), which is responsible for the PHIP magnetic field dependence. The
field dependence of polarization was considered in detail, general
peculiarities of PHIP were found, PHIP patterns were calculated for the
systems mentioned. Special attention was paid to the effects of field
switching on PHIP
Generating and sustaining long-lived spin states in 15N,15N′-azobenzene
Long-Lived spin States (LLSs) hold a great promise for sustaining non-thermal spin order and investigating various slow processes by Nuclear Magnetic Resonance (NMR) spectroscopy. Of special interest for such application are molecules containing nearly equivalent magnetic nuclei, which possess LLSs even at high magnetic fields. In this work, we report an LLS in trans-15N,15N′-azobenzene. The singlet state of the 15N spin pair exhibits a long-lived character. We solve the challenging problem of generating and detecting this LLS and further increase the LLS population by converting the much higher magnetization of protons into the 15N singlet spin order. As far as the longevity of this spin order is concerned, various schemes have been tested for sustaining the LLS. Lifetimes of 17 minutes have been achieved at 16.4 T, a value about 250 times longer than the longitudinal relaxation time of 15N in this magnetic field. We believe that such extended relaxation times, along with the photochromic properties of azobenzene, which changes conformation upon light irradiation and can be hyperpolarized by using parahydrogen, are promising for designing new experiments with photo-switchable long-lived hyperpolarization
Coherent transfer of nuclear spin polarization in field-cycling NMR experiments
Coherent polarization transfer effects in a coupled spin network have been
studied over a wide field range. The transfer mechanism is based on exciting
zero-quantum coherences between the nuclear spin states by means of non-
adiabatic field jump from high to low magnetic field. Subsequent evolution of
these coherences enables conversion of spin order in the system, which is
monitored after field jump back to high field. Such processes are most
efficient when the spin system passes through an avoided level crossing during
the field variation. The polarization transfer effects have been demonstrated
for N-acetyl histidine, which has five scalar coupled protons; the initial
spin order has been prepared by applying RF-pulses at high magnetic field. The
observed oscillatory transfer kinetics is taken as a clear indication of a
coherent mechanism; level crossing effects have also been demonstrated. The
experimental data are in very good agreement with the theoretical model of
coherent polarization transfer. The method suggested is also valid for other
types of initial polarization in the spin system, most notably, for spin
hyperpolarization
Spin mixing at level anti-crossings in the rotating frame makes high-field SABRE feasible
A new technique is proposed to carry out Signal Amplification By Reversible
Exchange (SABRE) experiments at high magnetic fields. SABRE is a method, which
utilizes spin order transfer from para-hydrogen to the spins of a substrate in
transient complexes using suitable catalysts. Such a transfer of spin order is
efficient at low magnetic fields, notably, in the Level Anti-Crossing (LAC)
regions. Here it is demonstrated that LAC conditions can also be fulfilled at
high fields in the rotating reference frame under the action of an RF-field.
Spin mixing at LACs allows one to polarize substrates at high fields as well;
the achievable NMR enhancements are around 360 for the ortho-protons of
partially deuterated pyridine used as a substrate and around 700 for H2 and
substrate in the active complex with the catalyst. High-field SABRE effects
have also been found for several other molecules containing a nitrogen atom in
the aromatic ring
High resolution NMR study of T1 magnetic relaxation dispersion. IV. Proton relaxation in amino acids and Met-enkephalin pentapeptide
Nuclear Magnetic Relaxation Dispersion (NMRD) of protons was studied in the
pentapeptide Met-enkephalin and the amino acids, which constitute it.
Experiments were run by using high-resolution Nuclear Magnetic Resonance (NMR)
in combination with fast field-cycling, thus enabling measuring NMRD curves
for all individual protons. As in earlier works, Papers I–III, pronounced
effects of intramolecular scalar spin-spin interactions, J-couplings, on spin
relaxation were found. Notably, at low fields J-couplings tend to equalize the
apparent relaxation rates within networks of coupled protons. In Met-
enkephalin, in contrast to the free amino acids, there is a sharp increase in
the proton T1-relaxation times at high fields due to the changes in the regime
of molecular motion. The experimental data are in good agreement with theory.
From modelling the relaxation experiments we were able to determine motional
correlation times of different residues in Met-enkephalin with atomic
resolution. This allows us to draw conclusions about preferential conformation
of the pentapeptide in solution, which is also in agreement with data from
two-dimensional NMR experiments (rotating frame Overhauser effect
spectroscopy). Altogether, our study demonstrates that high-resolution NMR
studies of magnetic field-dependent relaxation allow one to probe molecular
mobility in biomolecules with atomic resolution
Towards a common description of liquid-state and solid-state cases
Chemically Induced Dynamic Nuclear Polarization (CIDNP) is an efficient method
of creating non-equilibrium polarization of nuclear spins by using chemical
reactions, which have radical pairs as intermediates. The CIDNP effect
originates from (i) electron spin-selective recombination of radical pairs and
(ii) the dependence of the inter-system crossing rate in radical pairs on the
state of magnetic nuclei. The CIDNP effect can be investigated by using
Nuclear Magnetic Resonance(NMR) methods. The gain from CIDNP is then two-fold:
it allows one to obtain considerable amplification of NMR signals; in
addition, it provides a very useful tool for investigating elusive radicals
and radical pairs. While the mechanisms of the CIDNP effect in liquids are
well established and understood, detailed analysis of solid-state CIDNP
mechanisms still remains challenging; likewise a common theoretical frame for
the description of CIDNP in both solids and liquids is missing. Difficulties
in understanding the spin dynamics that lead to the CIDNP effect in the solid-
state case are caused by the anisotropy of spin interactions, which increase
the complexity of spin evolution. In this work, we propose to analyze CIDNP in
terms of level crossing phenomena, namely, to attribute features in the CIDNP
magnetic field dependence to Level Crossings (LCs) and Level Anti-Crossings
(LACs) in a radical pair. This approach allows one to describe liquid-state
CIDNP; the same holds for the solid-state case where anisotropic interactions
play a significant role in CIDNP formation. In solids, features arise
predominantly from LACs, since in most cases anisotropic couplings result in
perturbations, which turn LCs into LACs. We have interpreted the CIDNP
mechanisms in terms of the LC/LAC concept. This consideration allows one to
find analytical expressions for a wide magnetic field range, where several
different mechanisms are operative; furthermore, the LAC description gives a
way to determine CIDNP sign rules. Thus, LCs/LACs provide a consistent
description of CIDNP in both liquids and solids with the prospect of
exploiting it for the analysis of short-lived radicals and for optimizing the
polarization level
Magnetic field dependent long-lived spin states in amino acids and dipeptides
Magnetic field dependence of long-lived spin states (LLSs) of the β-CH2
protons of aromatic amino acids was studied. LLSs are spin states, which are
immune to dipolar relaxation, thus having lifetimes far exceeding the
longitudinal relaxation times; the simplest example of an LLS is given by the
singlet state of two coupled spins. LLSs were created by means of the photo-
chemically induced dynamic nuclear polarization technique. The systems studied
were amino acids, histidine and tyrosine, with different isotopomers. For
labeled amino acids with the α-CH and aromatic protons substituted by
deuterium at low fields the LLS lifetime, TLLS, for the β-CH2 protons was more
than 40 times longer than the T1-relaxation time. Upon increasing the number
of protons the ratio TLLS/T1 was reduced; however, even in the fully
protonated amino acids it was about 10; that is, the long-lived mode was still
preserved in the system. In addition, the effect of paramagnetic impurities on
spin relaxation was studied; field dependencies of T1 and TLLS were measured.
LLSs were also formed in tyrosine-containing dyads; a TLLS/T1 ratio of
[similar]7 was found, usable for extending the spin polarization lifetime in
such systems
Hyperpolarization of cis-15N,15N'-azobenzene by parahydrogen at ultralow magnetic fields
Development of the methods to exploit nuclear hyperpolarization and search for molecules whose nuclear spins can be efficiently hyperpolarized is an active area in nuclear magnetic resonance. Of particular interest are those molecules that have long nuclear relaxation times, making them to be suitable candidates as contrast agents in magnetic resonance imaging. In this work, we present a detailed study of SABRE SHEATH (Signal Amplification By Reversible Exchange in Shield Enabled Alignment Transfer to Heteronuclei) experiments of 15N,15N' azobenzene. In SABRE SHEATH experiments nuclear spins of the target are hyperpolarized by transfer of spin polarization from parahydrogen at ultralow fields during a reversible chemical process. The studied system is complicated, and we are concerned only about a subset of the data, presenting details for the molecules that experience fast chemical exchange at the catalytic complex and thus are involved in polarizing the free azobenzene. Azobenzene exists in two isomers trans- and cis-. We show that all nuclear spins in cis-azobenzene can be efficiently hyperpolarized by SABRE at suitable magnetic fields. Enhancement factors (relative to 9.4 T) reach several thousands of times for 15N spins and a few tens of times for the 1H spins. There are two approaches to observe either hyperpolarized magnetization of 15N/1H spins or hyperpolarized singlet order of the 15N spin pair. We compare these approaches and present the field dependencies of SABRE experiments for them. No hyperpolarization of trans 15N,15N' azobenzene was observed. The results presented here will be useful for further experiments where hyperpolarized cis-15N,15N' azobenzene is switched by light to trans 15N,15N' azobenzene for storing the produced hyperpolarization in the long-lived spin state of the 15N pair of trans-15N,15N' azobenzene
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