Three-dimensional magnetic stripes require slow cooling in fast-spread lower ocean crust.

Earth's magnetic field is recorded as oceanic crust cools, generating lineated magnetic anomalies that provide the pattern of polarity reversals for the past 160 million years1. In the lower (gabbroic) crust, polarity interval boundaries are proxies for isotherms that constrain cooling and hence crustal accretion. Seismic observations2-4, geospeedometry5-7 and thermal modelling8-10 of fast-spread crust yield conflicting interpretations of where and how heat is lost near the ridge, a sensitive indicator of processes of melt transport and crystallization within the crust. Here we show that the magnetic structure of magmatically robust fast-spread crust requires that crustal temperatures near the dike-gabbro transition remain at approximately 500 degrees Celsius for 0.1 million years. Near-bottom magnetization solutions over two areas, separated by approximately 8 kilometres, highlight subhorizontal polarity boundaries within 200 metres of the dike-gabbro transition that extend 7-8 kilometres off-axis. Oriented samples with multiple polarity components provide direct confirmation of a corresponding horizontal polarity boundary across an area approximately one kilometre wide, and indicate slow cooling over three polarity intervals. Our results are incompatible with deep hydrothermal cooling within a few kilometres of the axis2,7 and instead suggest a broad, hot axial zone that extends roughly 8 kilometres off-axis in magmatically robust fast-spread ocean crust.

Primitive layered gabbros from fast-spreading lower oceanic crust.

Three-quarters of the oceanic crust formed at fast-spreading ridges is composed of plutonic rocks whose mineral assemblages, textures and compositions record the history of melt transport and crystallization between the mantle and the sea floor. Despite the importance of these rocks, sampling them in situ is extremely challenging owing to the overlying dykes and lavas. This means that models for understanding the formation of the lower crust are based largely on geophysical studies and ancient analogues (ophiolites) that did not form at typical mid-ocean ridges. Here we describe cored intervals of primitive, modally layered gabbroic rocks from the lower plutonic crust formed at a fast-spreading ridge, sampled by the Integrated Ocean Drilling Program at the Hess Deep rift. Centimetre-scale, modally layered rocks, some of which have a strong layering-parallel foliation, confirm a long-held belief that such rocks are a key constituent of the lower oceanic crust formed at fast-spreading ridges. Geochemical analysis of these primitive lower plutonic rocks--in combination with previous geochemical data for shallow-level plutonic rocks, sheeted dykes and lavas--provides the most completely constrained estimate of the bulk composition of fast-spreading oceanic crust so far. Simple crystallization models using this bulk crustal composition as the parental melt accurately predict the bulk composition of both the lavas and the plutonic rocks. However, the recovered plutonic rocks show early crystallization of orthopyroxene, which is not predicted by current models of melt extraction from the mantle and mid-ocean-ridge basalt differentiation. The simplest explanation of this observation is that compositionally diverse melts are extracted from the mantle and partly crystallize before mixing to produce the more homogeneous magmas that erupt.

Partnering with your library to strengthen nursing research.

Nurses must know how to locate and evaluate health information to optimize their professional practice. However, much of the information available online and in print lacks credibility, and navigating professional research databases can prove complex. As more nursing students and nurse educators move from centralized, brick-and-mortar campuses to satellite locations and online courses, the need for adaptable library services becomes pronounced. This article describes a program that serves decentralized nursing students and nurse educators. Relationship building, one-to-one contact, and flexibility are program hallmarks. Services provided by the program and evaluation methods are discussed, and ways of building collaboration are recommended.

Is insertion of a plastic stent better and safer than epinephrine injection in post sphincterotomy bleeding?

OBJECTIVES: Epinephrine injection is the therapy of first choice in post sphincterotomy bleeding (PSB), but may not be efficient in all cases and can cause postprocedural myocardial infarction. Plastic stent insertion (PSI) may be a better treatment. The aim of this retrospective study was to compare epinephrine injection with PSI with respect to efficacy and safety. METHODS: Clinical success, number of reinterventions and hospital stays after therapy, postprocedural myocardial infarction, bilirubin increase, and pancreatitis as well as factors influencing PSB were analyzed. RESULTS: Seventy-nine PSBs in 5798 endoscopic retrograde cholangiopancreaticographies (ERCPs) from August 2002 through October 2018 were treated by epinephrine injection, PSI or both (n = 34, 30, 15). Clinical success of PSB therapy showed no difference: 33/34 (97%), 30/30 (100%), 14/15 (93%). Reinterventions were more frequent (n = 30 versus n = 1; P ≤ 0.0001) and hospital stay was longer [median: 3 (2-10) versus 2 (1-3) days; P = 0.0357] in patients who received PSI (versus epinephrine injection). Postprocedural adverse events were very rare: bilirubin increase (1/2/0) and pancreatitis (0/2/1). Intraprocedural episodes of hypertension (≥180 mmHg) were documented in 45-54%. CONCLUSIONS: Epinephrine injection is better than PSI in PSB. PSI may be an adequate treatment in patients with otherwise indicated stent insertion. Intraprocedural episodes of hypertension may be a risk factor for PSB.

Nurses working with librarians.

Librarians can offer nurses a great deal of assistance in locating information to support their clinical practice. This column outlines places nurses can find librarians who specialize in health care information. High-quality health information tools nurses can easily access online are also featured.

Local anesthetics as antimicrobial agents: a review.

BACKGROUND: Since the introduction of cocaine in 1884, local anesthetics have been used as a mainstay of pain management. However, numerous studies over the past several decades have elucidated the supplemental role of local anesthetics as antimicrobial agents. In addition to their anesthetic properties, medications such as bupivacaine and lidocaine have been shown to exhibit bacteriostatic, bactericidal, fungistatic, and fungicidal properties against a wide spectrum of microorganisms. METHODS: A comprehensive literature search was conducted using MEDLINE 1950-present for in vitro and in vivo studies pertaining to the antimicrobial activity of various local anesthetics on a broad range of bacterial and fungal pathogens. Studies testing the effect on microbial growth inhibition of local anesthetics alone and in combination with other agents, such as preservatives and other medications, as well as the effect of conditions such as concentration and temperature, were included for review. Outcome measures included colony counts, area-under-the-curve and time-kill curve calculations, minimum inhibitory concentrations, and post-antibiotic effect. RESULTS: Evidence suggests that local anesthetics as a class possess inherent antimicrobial properties against a wide spectrum of human pathogens. Multiple local anesthetics at concentrations typically used in the clinical setting (e.g., bupivacaine 0.125%-0.75%; lidocaine 1%-3%) inhibit the growth of numerous bacteria and fungi under various conditions. Different local anesthetics showed various degrees of antimicrobial capacity; bupivacaine and lidocaine, for example, inhibit growth to a significantly greater extent than does ropivacaine. Greater concentrations, longer exposure, and higher temperature each correlate with a proportional increase in microbial growth inhibition. Addition of other agents to the anesthetic solutions, such as preservatives, opioids, or intravenous anesthetics such as propofol, modify the antimicrobial activity via either synergistic or antagonistic action. Limited studies attribute the mechanism of action of antimicrobial activity of local anesthetics to a disruption of microbial cell membrane permeability, leading to leakage of cellular components and subsequent cell lysis. CONCLUSIONS: Local anesthetics not only serve as agents for pain control, but possess antimicrobial activity as well. In such a capacity, local anesthetics can be considered as an adjunct to traditional antimicrobial use in the clinical or laboratory setting. Additionally, caution should be exercised when administering local anesthetics prior to diagnostic procedures in which culture specimens are to be obtained, as the antimicrobial activity of the local anesthetic could lead to false-negative results or suboptimal culture yields.

Dating the growth of oceanic crust at a slow-spreading ridge.

Nineteen uranium-lead zircon ages of lower crustal gabbros from Atlantis Bank, Southwest Indian Ridge, constrain the growth and construction of oceanic crust at this slow-spreading midocean ridge. Approximately 75% of the gabbros accreted within error of the predicted seafloor magnetic age, whereas approximately 25% are significantly older. These anomalously old samples suggest either spatially varying stochastic intrusion at the ridge axis or, more likely, crystallization of older gabbros at depths of approximately 5 to 18 kilometers below the base of crust in the cold, axial lithosphere, which were uplifted and intruded by shallow-level magmas during the creation of Atlantis Bank.