Static and dynamic magnetic properties of Co nanoparticles.

Co nanoparticles have been synthesized using wet-chemical methods. As-synthesized particles show a sharp low temperature peak in zero-field cooled (ZFC) magnetization well below the blocking transition temperature and this feature is associated with surface spin disorder. We have investigated the dynamic magnetic properties of Co using ac susceptibility and resonant RF transverse susceptibility (TS). We also studied the memory and relaxation effects in these nanoparticle systems. From these measurements we show a typical blocking behavior of an assembly of superparamagnetic nanoparticles with a wide distribution of blocking temperatures. The transverse susceptibility measurements on these particles show the presence of anisotropy even above the blocking temperature. The role of surface anisotropy and the size distribution of the particles on the observed memory and magnetic relaxation effects are discussed.

Observation of a new magnetic anomaly below the ferromagnetic Curie temperature in Yb14MnSb11.

Yb14MnSb11 is an unusual ferromagnet with a Curie temperature of 52 +/- 1 K. Recent optical, Hall, magnetic, and thermodynamic measurements indicate that Yb14MnSb11 may be a rare example of an underscreened Kondo lattice. We report the first experimental observation of a new magnetic anomaly in this system at around 47 K, a few degrees below T(c). Systematic investigations of the ac and dc susceptibilities of Yb14MnSb11 single crystals reveal features associated with possible spin reorientation at this temperature. This new anomaly is extremely sensitive to the applied measurement field and is absent in temperature-dependent dc magnetization data for fields above 50 Oe. The origin of this could be due to decoupling of two distinct magnetic sublattices associated with MnSb4 tetrahedra.

Chemically fabricated magnetic quantum dots of InP:Mn.

Quantum dots of InP:Mn are chemically prepared by following hot colloidal nanochemistry with starting precursors that obviate the need for external surfactant. These quantum dots are uniform spheres with 3-nm diameters; they are crystalline, photoluminescent, and magnetic. The crystallographic and optical properties are similar to those of undoped InP nanocrystallites, while the magnetism is consistent with the ferromagnetic response observed in a class of diluted magnetic semiconductors. Because of the ultrafine sizes, the sample shows superparamagnetic behavior, whereas ferromagnetic hysteresis loops are clearly seen below the blocking temperature. Structural characterization and analysis confirm that the magnetism in these quantum dots is not due to segregated binary MnP or MnO phases and that they truly represent a homogeneous dilute magnetic semiconductor.

Nanocomposite magneto-rheological fluids with uniformly dispersed Fe nanoparticles.

A systematic study of the magnetic and rheological properties of magneto-rheological (MR) fluids containing micron-size and nano-size iron particles is presented. The MR fluids were prepared with hydraulic oil as the carrier liquid and lecithin as an effective surfactant medium that promotes uniform particle dispersion. Magnetic measurements on micron-, hybrid-(nano + micron), and nano-MR fluids clearly indicate that the partial replacement of the micro-size particles by nanoparticles results in a better suspension and robust chain formation under applied external magnetic fields. For nano-MR fluids, the measured yield stress was found to be lower than micron-MR fluids. However, better flow properties and sharper magnetic switching make nanoparticle-based MR fluids appealing for microfluidics device applications where higher yield stress is not required.

Severity of intrathoracic injuries associated with first rib fractures.

The benign condition of isolated first rib fracture is compared with the severity of intrathoracic injuries resulting from first rib fracture associated with multiple rib injuries. Seventy-five patients with 90 first rib fractures were divided into two groups. Group 1 (n = 13) included those with isolated first rib fractures and Group 2 (n = 62), those with first-rib fractures associated with multiple rib injuries. In Group 1 patients, intrathoracic injuries were mild with no major vascular injuries. Conversely, Group 2 patients sustained severe intrathoracic injury, 58% of them with aortic injury. Stress is placed on early diagnosis, assigning of priority to associated injuries, and early operative intervention.

Ileocaecal tuberculosis.

A retrospective study of 92 cases of ileocaecal tuberculosis, carried out at the Institute Hospital, New Delhi, is reported. The maximum incidence of the disease appeared to be between the ages of 20 and 40 years. There were 57 females and 35 males in the series. The majority of patients had symptoms for more than a year before they presented for treatment. Varying grades of intestianl obstruction constituted the usual clinical presentation, 44% of patients having subacute and 16% acute intestinal obstruction. Perianal fistula and abscesses were not seen. Most patients had no evidence of pulmonary tuberculosis. Barium X-ray studies were very helpful in the diagnosis. Bowel resection or short-circuiting gave very satisfactory results.

Carcinoma of the stomach.

Seventy-five cases of stomach carcinoma were analyzed. The incidence was highest between 41 and 50 years of age. Male to female ratio was 4:1. The average duration of symptoms was one year. There was no correlation between incidence and the dietary and smoking habits of the patients. Epigastric pain was the commonest complaint followed byanorexis, vomiting and loss of weight. Anemia was the commonest finding. Epigastric mass was present in nearly 50% of cases. Pyloric obstruction was common. Upper gastrointestinal x-ray studies were rewarding. Occult blood was often found in the stools. The majority of patients were about equally distributed between blood groups A and O. Many patients had no or low acid levels but 7.5% had normal or high acid levels. At operation, the growth was commonly found near the pylorus. Diffuse involvement was infrequent. Curative surgery could be done in only 20% of cases. One-third of the patients had palliative gastrojejunostomy. The operative mortality and morbidity were high. The overall five-year survival was only 5%.