The observed correlation between the EMC effect and the contribution of short-range correlations (SRCs) in nuclei suggests that the modification of the quark distributions of bound protons and ...neutrons might occur within SRCs. This raises the possibility that the EMC effect may have an isospin dependence arising from the np dominance of SRCs. We discuss previous attempts to test this possibility and perform a new analysis of existing data. We find no experimental support for the observation of an isospin dependence of the EMC effect.
Hard probes of short-range nucleon–nucleon correlations Arrington, J.; Higinbotham, D.W.; Rosner, G. ...
Progress in particle and nuclear physics,
October 2012, 2012-10-00, 2012-10-01, Letnik:
67, Številka:
4
Journal Article
Recenzirano
Odprti dostop
One of the primary goals of nuclear physics is providing a complete description of the structure of atomic nuclei. While mean-field calculations provide detailed information on the nuclear shell ...structure for a wide range of nuclei, they do not capture the complete structure of nuclei, in particular the impact of small, dense structures in nuclei. The strong, short-range component of the nucleon–nucleon potential yields hard interactions between nucleons which are close together, generating a high-momentum tail to the nucleon momentum distribution, with momenta well in excess of the Fermi momentum. This high-momentum component of the nuclear wave-function is one of the most poorly understood parts of nuclear structure.
Utilizing high-energy probes, we can isolate scattering from high-momentum nucleons, and use these measurements to examine the structure and impact of short-range nucleon–nucleon correlations. Over the last decade we have moved from looking for evidence of such short-range structures to mapping out their strength in nuclei and examining their isospin structure. This has been made possible by high-luminosity and high-energy accelerators, coupled with an improved understanding of the reaction mechanism issues involved in studying these structures. We review the general issues related to short-range correlations, survey recent experiments aimed at probing these short-range structures, and lay out future possibilities to further these studies.
We review the role of two-photon exchange (TPE) in electron–hadron scattering, focusing in particular on hadronic frameworks suitable for describing the low and moderate
Q
2
region relevant to most ...experimental studies. We discuss the effects of TPE on the extraction of nucleon form factors and their role in the resolution of the proton electric to magnetic form factor ratio puzzle. The implications of TPE on various other observables, including neutron form factors, electroproduction of resonances and pions, and nuclear form factors, are summarized. Measurements seeking to directly identify TPE effects, such as through the angular dependence of polarization observables, nonlinear
ε
contributions to the cross sections, and via
e
+
p
to
e
−
p
cross section ratios, are also outlined. In the weak sector, we describe the role of TPE and
γ
Z
interference in parity-violating electron scattering, and assess their impact on the extraction of the strange form factors of the nucleon and the weak charge of the proton.
► We review two-photon exchange (TPE) in electron–hadron scattering. ► TPE resolves the proton electric to magnetic form factor discrepancy. ► TPE can be tested in other observables such as
e
+
p
to
e
−
p
ratios.► Photon-
Z
boson exchange impacts extraction of the proton weak charge.
We present a detailed analysis of the uncertainty in the neutron F(2n) structure function extracted from inclusive deuteron and proton deep-inelastic scattering data. The analysis includes ...experimental uncertainties as well as uncertainties associated with the deuteron wave function, nuclear smearing, and nucleon off-shell corrections. Correctly accounting for the Q(2) dependence of the data and calculations and restricting the nuclear corrections to microscopic models of the deuteron, we find a significantly smaller uncertainty in the extracted F(2n)/F(2p) ratio than in previous analyses. In addition to yielding an improved extraction of the neutron structure function, this analysis also provides an important baseline that can be compared to future, model-independent extractions of neutron structure to examine nuclear medium effects in the deuteron.
A systematic series of 16 amphiphilic bottlebrush block copolymers (BCPs) containing polystyrene and poly(N-acryloylmorpholine) (PACMO) side chains were prepared by a combination of atom-transfer ...radical polymerization (ATRP), photoiniferter polymerization, and ring-opening metathesis polymerization (ROMP). The grafting-through method used to prepare the polymers enabled a high degree of control over backbone and side-chain molar masses for each block. Surface tension measurements on the self-assembled amphiphilic bottlebrush BCPs in water revealed an ultralow critical micelle concentration (cmc), 1–2 orders of magnitude lower than linear BCP analogues on a molar basis, even for micelles with >90% PACMO content. Combined with coarse-grained molecular dynamics simulations, fitting of small-angle neutron scattering traces (SANS) allowed us to evaluate solution conformations for individual bottlebrush BCPs and micellar nanostructures for self-assembled macromolecules. Bottlebrush BCPs showed an increase in anisotropy with increasing PACMO content in toluene-d 8, which is a good solvent for both blocks, reflecting an extended conformation for the PACMO block. SANS traces of bottlebrush BCPs assembled into micelles in D2O, a selective solvent for PACMO, were fitted to a core–shell–shell model, suggesting the presence of a partially hydrated inner shell. Results showed an average micelle diameter of 40 nm with combined shell diameters ranging from 16 to 18 nm. A general trend of increased stability of micelles (i.e., resistance to precipitation) was observed with increases in PACMO content. These results demonstrate the stability of bottlebrush polymer micelles, which self-assemble to form spherical micelles with ultralow (<70 nmol/L) cmc’s across a broad range of compositions.
Background Previously, the Dialysis Outcomes and Practice Patterns Study (DOPPS) has shown large international variations in vascular access practice. Greater mortality risks have been seen for ...hemodialysis (HD) patients dialyzing with a catheter or graft versus a native arteriovenous fistula (AVF). To further understand the relationship between vascular access practice and outcomes, we have applied practice-based analyses (using an instrumental variable approach) to decrease the treatment-by-indication bias of prior patient-level analyses. Study Design A prospective observational study of HD practices. Setting & Participants Data collected from 1996 to 2004 from 28,196 HD patients from more than 300 dialysis units participating in the DOPPS in 12 countries. Predictor or Factor Patient-level or case-mix–adjusted facility-level vascular access use. Outcomes/Measurements Mortality and hospitalization risks. Results After adjusting for demographics, comorbid conditions, and laboratory values, greater mortality risk was seen for patients using a catheter (relative risk, 1.32; 95% confidence interval, 1.22 to 1.42; P < 0.001) or graft (relative risk, 1.15; 95% confidence interval, 1.06 to 1.25; P < 0.001) versus an AVF. Every 20% greater case-mix–adjusted catheter use within a facility was associated with 20% greater mortality risk (versus facility AVF use, P < 0.001); and every 20% greater facility graft use was associated with 9% greater mortality risk ( P < 0.001). Greater facility catheter and graft use were both associated with greater all-cause and infection-related hospitalization. Catheter and graft use were greater in the United States than in Japan and many European countries. More than half the 36% to 43% greater case-mix–adjusted mortality risk for HD patients in the United States versus the 5 European countries from the DOPPS I and II was attributable to differences in vascular access practice, even after adjusting for other HD practices. Vascular access practice differences accounted for nearly 30% of the greater US mortality compared with Japan. Limitations Possible existence of unmeasured facility- and patient-level confounders that could impact the relationship of vascular access use with outcomes. Conclusions Facility-based analyses diminish treatment-by-indication bias and suggest that less catheter and graft use improves patient survival.
Novel targeted and immunotherapeutic agents have revolutionized systemic melanoma management. We note differing rates of distant brain control as well as overall survival following systemic treatment ...and stereotactic radiosurgery (SRS) in melanoma brain metastases management. These data support further research to determine the potential synergistic effect between these agents with SRS.
The effect of immunologic and targeted agents on intracranial response rates in patients with melanoma brain metastases (MBMs) is not yet clearly understood. This report analyzes outcomes of intact MBMs treated with single-session stereotactic radiosurgery (SRS) and anti-PD-1 therapy, anti-CTLA-4 therapy, BRAF/MEK inhibitors(i), BRAFi, or conventional chemotherapy.
Patients were included if MBMs were treated with single-session SRS within 3 months of receiving systemic therapy. The primary end point of this study was distant MBM control. Secondary end points were local MBM control defined as a >20% volume increase on follow-up MRI, systemic progression-free survival, overall survival (OS) from both SRS and cranial metastases diagnosis, and neurotoxicity. Images were reviewed alongside two neuro-radiologists at our institution.
Ninety-six patients were treated to 314 MBMs over 119 SRS treatment sessions between January 2007 and August 2015. No significant differences were noted in age (P = 0.27), gender (P = 0.85), treated gross tumor volume (P = 0.26), or the diagnosis-specific graded prognostic assessment (P = 0.51) between the treatment cohorts. Twelve-month Kaplan–Meier (KM) distant MBM control rates were 38%, 21%, 20%, 8%, and 5% (P = 0.008) for SRS with anti-PD-1 therapies, anti-CTLA-4 therapy, BRAF/MEKi, BRAFi, and conventional chemotherapy, respectively. No significant differences were noted in the KM local MBM control rates among treatment groups (P = 0.25). Treatment with anti-PD-1 therapy, anti-CTLA-4 therapy, or BRAF/MEKi significantly improved OS on both univariate and multivariate analyses when compared with conventional chemotherapy.
In our institutional analysis of patients treated with SRS and various systemic immunologic and targeted melanoma agents, significant differences in distant MBM control and OS are noted. Prospective evaluation of the potential synergistic effect between these agents and SRS is warranted.
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