Λ-Nucleon Charge-Symmetry-Breaking Interaction. I. Separable Potentials

The existence of a charge-symmetry-breaking (CSB) term in the lambda-nucleon (Λ−N) interaction is shown to produce an admixture of a T=1 state to the predominant isospin singlet state in ΛH3. The present analysis shows that a CSB term constructed to fit light hypernuclear and Λ−p scattering data is poorly determined (∼4%-25% of the total Λ−p singlet and ∼4%-15% of the total Λ−p triplet interaction), but is strongly correlated with the Λ-separation energy, BΛ, from ΛH3, and that isospin mixing in ΛH3 can lead to significant adjustments of the deduced Λ−N interaction strengths. The mixed-symmetry T=0 state in ΛH3 is seen to have a small effect. Data employed include Λ−p total cross sections, σ(Λp), for total c.m. energy Ec.m.MeV, published values of BΛ, and a theoretical determination by Herndon and Tang of the relative magnitudes of the Λ−N potentials responsible for the mean binding and the ground-state splitting of ΛHe4 and ΛHe4. The two hypotheses that the spin, I, of ΛHe4 is 0 and 1 are studied. Nonlocal separable, spin-dependent central interactions of the Yamaguchi form are used, and all range parameters in the Λ−N interaction are constrained to be equal. A search of fits to σ(Λp) is made with intrinsic ranges in the interval 1.5 F to 2.3 F. Self-consistent CSB potentials are found for I=0 and I=1. The deduced singlet Λ−p CSB interaction is attractive in all cases, in disagreement with predictions of the SU3 particle-mixing model of Downs

Λ-Nucleon Charge-Symmetry-Breaking Interaction. II. Rank-2 Potentials

A potential model of the Λ−N interaction containing short-range repulsions is constructed to study charge-symmetry-breaking (CSB). Rank-2 nonlocal central potentials and a rank-1 approximation to them (referred to as UPAA) are required to fit low-energy Λ−p scattering cross sections, the Λ-separation energy (BΛ) from ΛH3, and a dimensionless parameter which partially characterizes the CSB part of the binding-energy difference between ΛH4 and ΛH4. In a scan of these data, a class of potentials with acceptable x2 fits is found. Repulsions are seen to reduce significantly the lower limits of the singlet and triplet CSB strengths required in the entire data scan, from the CSB found earlier without including repulsions. In particular, for the largest value of BΛ used, 0.25 MeV, qualitative agreement with Downs\u27s SU3 model of CSB is attained, in that the Λ−p CSB singlet interaction can be repulsive. This conclusion also holds for the UPAA, with an indication that a short-range weakening of Λ−N attraction has an effect similar to a Λ−N repulsion. Effects of isospin mixing in ΛH3 are taken into account. The Λ−N potentials resulting from this analysis are seen to vary in a systematic way within the statistical spread of available data

Long-Term Effects of Cathodic Protection on Prestressed Concrete Bridge Components

DTFH61-92-C-00058While cathodic protection effectively reduces or stops ongoing corrosion of reinforcing steel in concrete, applicability of this technology to prestressing steel has been limited because of concerns of possible bond loss and hydrogen embrittlement. Within this context the present research was intended as a comprehensive, multifaceted undertaking to elevate the understanding of prestressed concrete cathodic protection to the same level as for reinforced concrete. The experimental part of the program involved three approaches: 1) constant extension rate tests (CERT) upon straight tendon wire, 2) monitoring of cathodically polarized prestressed beams for both bond loss and hydrogen embrittlement, and 3) concrete block pullout tests involving both tendon and wire. Findings to date include the following: 1) High chromium bearing microalloyed prestressing steel is more susceptible to embrittlement than ordinary steel, and the previously proposed -0.90 v (SCE) lower potential limit is not conservative in this case; 2) Prestressed concrete structures can be qualified for cathodic protection based upon the amount of uniform and localized corrosion wire cross section loss; 3) Loss of bond within the anticipated remaining service life of most prestressed concrete structures should not be a concern provided current density is within the normal range and is not locally concentrated. These and related findings are evaluated within the context of standards for prestressing steel and criteria for cathodic protection

Description of the two-nucleon system on the basis of the Bargmann representation of the S matrix

For the effective-range function $k\cot \delta$, a pole approximation that involves a small number of parameters is derived on the basis of the Bargmann representation of the $S$ matrix. The parameters of this representation, which have a clear physical meaning, are related to the parameters of the Bargmann $S$ matrix by simple equations. By using a polynomial least-squares fit to the function $k\cot \delta$ at low energies, the triplet low-energy parameters of neutron-proton scattering are obtained for the latest experimental data of Arndt et al. on phase shifts. The results are $a_{t}=5.4030$fm, $r_{t}=1.7494$fm, and $v_{2}=0.163$fm$^{3}$. With allowance for the values found for the low-energy scattering parameters and for the pole parameter, the pole approximation of the function $k\cot \delta$ provides an excellent description of the triplet phase shift for neutron-proton scattering over a wide energy range ($T_{\text{lab}}\lesssim 1000$MeV), substantially improving the description at low energies as well. For the experimental phase shifts of Arndt et al., the triplet shape parameters $v_{n}$ of the effective-range expansion are obtained by using the pole approximation. The description of the phase shift by means of the effective-range expansion featuring values found for the low-energy scattering parameters proves to be fairly accurate over a broad energy region extending to energy values approximately equal to the energy at which this phase shift changes sign, this being indicative of a high accuracy and a considerable value of the effective-range expansion in describing experimental data on nucleon-nucleon scattering. The properties of the deuteron that were calculated by using various approximations of the effective-range function comply well with their experimental values.Comment: 39 pages, 3 figure

The Oldest Case of Decapitation in the New World (Lapa do Santo, East-Central Brazil)

We present here evidence for an early Holocene case of decapitation in the New World (Burial 26), found in the rock shelter of Lapa do Santo in 2007. Lapa do Santo is an archaeological site located in the Lagoa Santa karst in east-central Brazil with evidence of human occupation dating as far back as 11.7-12.7 cal kyBP (95.4% interval). An ultra-filtered AMS age determination on a fragment of the sphenoid provided an age range of 9.1-9.4 cal kyBP (95.4% interval) for Burial 26. The interment was composed of an articulated cranium, mandible and first six cervical vertebrae. Cut marks with a v-shaped profile were observed in the mandible and sixth cervical vertebra. The right hand was amputated and laid over the left side of the face with distal phalanges pointing to the chin and the left hand was amputated and laid over the right side of the face with distal phalanges pointing to the forehead. Strontium analysis comparing Burial 26's isotopic signature to other specimens from Lapa do Santo suggests this was a local member of the group. Therefore, we suggest a ritualized decapitation instead of trophy-taking, testifying for the sophistication of mortuary rituals among hunter-gatherers in the Americas during the early Archaic period. In the apparent absence of wealth goods or elaborated architecture, Lapa do Santo's inhabitants seemed to use the human body to express their cosmological principles regarding death

Brazilian coral reefs in a period of global change: A synthesis

Abstract Brazilian coral reefs form structures significantly different from the well-known reef models, as follows: (i) they have a growth form of mushroom-shaped coral pinnacles called "chapeirões", (ii) they are built by a low diversity coral fauna rich in endemic species, most of them relic forms dating back to the Tertiary, and (iii) the nearshore bank reefs are surrounded by siliciclastic sediments. The reefs are distributed in the following four major sectors along the Brazilian coast: the northern, the northeastern and the eastern regions, and the oceanic islands, but certain isolated coral species can be found in warmer waters in embayments of the southern region. There are different types of bank reefs, fringing reefs, isolated "chapeirões" and an atoll present along the Brazilian coast. Corals, milleporids and coralline algae build the rigid frame of the reefs. The areas in which the major coral reefs occur correspond to regions in which nearby urban centers are experiencing accelerated growth, and tourism development is rapidly increasing. The major human effects on the reef ecosystem are mostly associated with the increased sedimentation due to the removal of the Atlantic rainforest and the discharge of industrial and urban effluents. The effects of the warming of oceanic waters that had previously affected several reef areas with high intensity coral bleaching had not shown, by the time of the 2010 event, any episodes of mass coral mortality on Brazilian reefs