James F. Marvin

A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: Some results from lake sediments

Abstract A new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility (χARM, i.e. specific ARM obtained in a 1 Oe steady field), which is particularly sensitive to the single domain (SD) and small pseudo-single domain (PSD) grains of the finer magnetite fraction. A second parameter, low-field susceptibility (χ), is relatively more sensitive to the coarser magnetite fraction (larger PSD and smaller multidomain (MD) grains). We can then obtain a measure of the ratio of coarse- to fine-grain magnetite for large numbers of samples by plotting χARversusχ. A simple idealized model based on sized magnetite samples is proposed to explain the use of the χARMversusχ plot for detecting relative grain-size changes in the magnetic content of natural materials. The sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of χARM and χ are used to test the model.The model is used to interpret the magnetic variations observed, and the interpretations are supported by high-field hysteresis measurements of the same sediments. The combination of the high-field hysteresis method of Day et al. [1] and the χARM vs. χ method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite. The χARMvs.χ method should be used as an intial means of identifying distinct groups of samples.The high-field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation.

Rock magnetism of remagnetized Paleozoic carbonates: Low-temperature behavior and susceptibility characteristics

We have conducted a new set of rock magnetic experiments on samples of remagnetized Paleozoic carbonates of eastern North America. These experiments were designed to investigate the origin of the unusual hysteresis behavior of these rocks, by evaluating (1) the importance of ferrimagnetic pyrrhotite as a remanence carrier, and (2) the sources of low-field susceptibility. Low-temperature measurements of saturation isothermal remanent magnetization (SIRM) indicate that the pyrrhotite magnetic transition at 32 K is absent in the Trenton and Onondaga limestones of New York. This transition is observed but poorly expressed in the Knox Group of east Tennessee: room-temperature SIRMs, cooled to 10 K in zero field, lose a small fraction of their intensity between 30 and 35 K. Samples from all three formations show a broad peak in IRM intensity at about 200 K, which is typical of pyrrhotite. In the Trenton and Onondaga samples, the ferrimagnetic component of low-field susceptibility is significantly larger than the ratio Mrs/Hcr, and is thus probably due dominantly to magnetite; in some of the Knox samples the reverse is true, suggesting an important pyrrhotite contribution. For all of the samples, the ferrimagnetic susceptibility, normalized by the saturation magnetization, is anomalously high, about a factor of 5 or 10 higher than the typical value for magnetite. We believe that this indicates a very substantial contribution from superparamagnetic particles. Strong frequency dependence of susceptibility and very high ratios of anhysteretic to saturation remanence confirm the importance of ultrafine particles, spanning the superparamagnetic—single-domain boundary. All three of these chemically remagnetized carbonates units exhibit the following properties, which have not previously been found together for any rock or synthetic analog, and which therefore appear to constitute a diagnostic set of rockmagnetic criteria for recognizing chemically-remagnetized rocks: Mrs/Ms ≈ 0.89 (Hcr/Hc)−0.6; kƒ/Ms ≈ 50 μm/A; ARM/SIRM ≈ 20%; ka/(Mrs/Hcr) ≈ 50.

A Rapid Method for Clinical Total Blood Volume Determination Using Radioactive Iodinated Human Serum Albumin (RIHSA)

Summary (1) A clinical laboratory procedure for directly measuring total circulating blood volume using RIHSA as the tracer agent has been described. (2) A series of 40 cases in whom total circulating blood volume was determined by this technic. (3) The advantages of this technic over the dye method have been discussed.

Use of small-amplitude paleomagnetic fluctuations for correlation and dating of continental climatic changes☆

Abstract Recent advances in field and laboratory methods have made possible the study of paleomagnetic fluctuations recorded with high resolution in lake sediments of relatively small amplitude and short period (∼102 years to ∼104 years). Foremost among these methods are sediment-coring techniques that allow azimuthally oriented long cores (⩽25 m) to be raised with small orientation errors (⩽ ± 3°), and the use of cryogenic magnetometers to measure weakly magnetized (M ⩽ 10−9 A m2) sediment samples accurately. With these methods, records of inclination, declination, and relative paleointensity (NRM/ARM) have been obtained in North America that span the last ∼20,000 years. Substantial agreement in declination and inclination features is seen on a scale of 103 km in North America for the last ∼10,000 years. These paleomagnetic features can be useful in determining the relative age of paleoclimatic features, particularly in those situations where 14C dating is unreliable. Similar agreement is seen for the last 4000 years between relative-paleointensity estimates obtained from Pennsylvania lake sediments and absolute-paleointensity estimates obtained from 14C-dated lava flows and potsherds from the western United States. Similar paleointensity fluctuations to those occurring from 0 to 4000 yr B.P. in the western United States are observed for the last 12,500 yr B.P. in lake sediments from New York and Pennsylvania. Such relative-paleointensity records from lake sediments, if independently confirmed, considerably extend the range and resolution of paleointensity data and have important implications for the study of secular-variation models, variations in atmospheric radiocarbon concentration, and the proposed relationships between geomagnetism and climate. An absolute secular-variation chronology for the varved sediments of Elk Lake, Minnesota, can be used to “date” magnetically the secular-variation records of unvarved sediments elsewhere in North America.

Biophysical studies of methods utilizing fluorescein and its derivatives to diagnose brain tumors.

The clinical use of sodium fluorescein as an aid in the diagnosis and localization of brain tumors has been previously documented (6, 11, 14). Briefly, the technic used at the present time is as follows: All patients subjected to craniotomy are injected immediately preceding surgery with 1.0 gram of sodium fluorescein. At operation, the cortex of the brain is examined under ultraviolet light. If a superficial tumor is present, it can be easily distinguished and its limits outlined by the presence of the yellow-green fluorescence typical of fluorescein. If the tumor is below the cortex and gives no indication of its presence on examination and palpation, brain needles are commonly used to probe for it and to obtain biospy material. With singular consistency, the presence or absence of fluorescence of the tissue fragments procured has been indicative of the presence or absence of abnormal tissue. Edematous brain tissue fluoresces slightly, and therefore, even if the surgeon does not strike the tumor directl...

The Use of Radioactive Phosphorus in the Diagnosis of Thyroid Cancer

Approximately twenty years ago it was first demonstrated that radioactive phosphorus (P32) uptake is selectively increased in malignant tissue (6, 11). During the past two decades P32 has been used to study numerous experimental and human tumors. Since thyroid cancer is often difficult to diagnose clinically, occasionally presenting a problem even to the pathologist examining microscopic sections, attention has been turned toward the diagnostic use of P32 uptake, particularly in solitary nodular and multinodular goiters. Method The P32-uptake test has been performed on a total of 61 patients with solitary nodular and multinodular goiters. These patients, including 47 women and 14 men, seventeen to seventy-seven years of age, were from the out-patient and in-patient services of the University of Minnesota Hospitals. They were given an oral dose of 500 microcuries of P32 in the form of sodium phosphate and were tested for uptake twenty-four hours later. With an eye-probe Geiger-Muller tube (Anton Laboratori...

Uptake and excretion of radioactive rose bengal dye in normal dogs.

Summary In normal adult mongrel dogs, radioactive rose bengal dye is rapidly removed from the blood stream with radioactivity reduced 50% in 5 to 10 minutes following intravenous injection of the dye. The liver takes up the dye rapidly, starting within 4 minutes, and excretes it quickly, as evidenced by appearance of dye in the bile 6 minutes after administration. Approximately 20% of the tagged dye passed through the bile in one hour. Urinary excretion is almost negligible, with approximately 0.1% of total dye present in the urine in 60 minutes. Renal, splenic, and pancreatic tissue levels of radioactivity are insignificant and probably represent amount of dye in the blood stream. Radioactivity over the duodenum is evident within the first hour and probably represents amount of dye excreted into the bile.

The effect of combined irradiation and chemotherapy on cancer growth with special reference to studies with folic acid analogues.

During the past four years we have been investigating the effects of chemicals on the radiation sensitivity of various biological systems. Particular emphasis has been given to the study of combined chemical and radiation therapy in the treatment of cancer. Chemical compounds which have been used include various porphyrins, folic acid analogues, sulfhydryl compounds, cortisone, sodium cyanide, and di-chlorovinyl-cysteine (1–4). Of these, the folic acid analogues have received special attention (5, 6) and are the subject of this report. By combining chemical and radiation therapy it may be possible to increase “therapeutic ratio,” which has been defined as the ratio of the radiosensitivity of tumor tissue relative to surrounding normal tissue (7). If the therapeutic ratio can be increased by chemical means, it would be possible to deliver a cancericidal dose of radiation with less damage to normal tissue. This may be accomplished either by sensitizing tumors to the effects of x-rays or by preferential prot...

Detection of minute gastrointestinal bleeding utilizing radioactive iron, Fe59.

Summary 1. Excretion patterns of intravenously administered radioactive iron in the stool of normal dogs and in dogs with histamine induced bleeding of the gastrointestinal tract have been compared. 2. Levels of stool radioactivity have been measured following intragastric administration of known amounts of isotope-labelled blood. 3. Radioactivity in the stool can be utilized for detection of occult bleeding. 4. Comparative evaluation following administration of known small quantities of isotope-labelled blood (Fe59) indicates definitely that this test is considerably more sensitive than the guaiac test.

Electronmicroscopy of the purified MM poliomyelitis virus.

Summary Electronmicroscopic studies of a preparation of purified MM Poliomyelitis virus show an uniformity of particle size in the range from 10 to 20 mμ with an average diameter of about 12 mμ.