Neuroendocrine Carcinoma of the Stomach: A Case Study

Gastric neuroendocrine carcinomas are rare and have a poor prognosis, and the diagnostic criteria for this disease have recently changed. We herein report a case of sporadic gastric neuroendocrine carcinoma. A 75-year-old man was referred to our hospital with epigastric pain. Endoscopic examination revealed a localized ulcerative lesion (diameter, 4 cm) at the upper stomach. The diagnosis on biopsy was neuroendocrine carcinoma. Total gastrectomy with D2 lymphadenectomy, splenectomy, and cholecystectomy was performed. Pathologically, the tumor infiltrated the subserosal layer, and 6/49 lymph nodes were involved. The tumor was uniform in shape and arranged in a rosette-like structure to form solid nests, with medium-sized, round-to-cuboid-shaped tumor cells and intense mitosis 46/10 HPF. It was positive for synaptophysin and chromogranin A, and the Ki-67 labeling index was 70–80%. The diagnosis of neuroendocrine carcinoma was made according to the WHO 2010 criteria. The patient was followed up for three years without recurrence

Interdot carrier and spin dynamics in a two-dimensional high-density quantum-dot array of InGaAs with quantum dots embedded as local potential minima

Interdot carrier and spin dynamics were studied in a two-dimensional array of high-density small quantum dots (SQDs) of InGaAs with an average diameter of 16 nm and a sheet density of 1.2 x 10(11) cm(-2), in which 24 nm diametric large QDs (LQDs) were embedded as local potential minima. We observed a delayed photoluminescence (PL) rise from the lower-lying LQD states and a considerably faster PL decay from the higher-lying SQD states, indicating carrier transfer from the two-dimensionally coupled SQDs into the LQDs. In addition, inverse carrier tunneling from the LQDs into the SQDs was thermally induced, which is characterized by the thermal activation energy between the LQDs and SQDs. Moreover, circularly polarized transient PL behavior from the SQD states exhibits a suppression of the spin polarization decay in the initial time region, depending on the excited spin density. This tentatively suppressed spin relaxation can be quantitatively explained by selective interdot transfer of minority-spin electrons from the SQDs into LQDs, when the majority spin states in both QDs are sufficiently populated by excited spins. These findings indicate that the high-density SQDs behave as the main emitters with suppressed spin relaxation, while the scattered LQDs with lower potential behave as the receivers of minority-spin electrons

Persistent High Polarization of Excited Spin Ensembles During Light Emission in Semiconductor Quantum-Dot-Well Hybrid Nanosystems

We demonstrate persistent high degrees of spin polarization (SPD) up to 70% during light emission in (In1-xGax) As quantum-dot-well (QD-QW) hybrid nanosystems, where QD excited states are laterally tunnel coupled through the adjacent two-dimensional QW potential depending on the QW thickness. Spinpolarized electrons are photo-excited by using circularly polarized light pulses. The decay time of spin relaxation, obtained by that of the SPD, is 70 times larger than the photoluminescence decay time. The temporally constant SPD is sustained by a selective transfer of minority spins among QDs after flipping from the majority spins, which is promoted by a moderate state filling of lower-energy spin sublevels in surrounding QDs. The spin transfer times are deduced as functions of the QW thickness and excited-spin density. These results can provide a precise control of lateral interdot spin-transfer dynamics and resultant suppression of spin relaxation in QD ensembles

Interdot spin transfer dynamics in laterally coupled excited spin ensemble of high-density InGaAs quantum dots

Interdot spin transfer dynamics is studied in a laterally coupled excited spin ensemble of high-density InGaAs quantum dots (QDs). We observe a rise time of the photoluminescence intensity of similar to 100 ps and a simultaneous increase in the spin polarization of the excited spin ensemble, indicating spin injection from higher-energy levels in smaller QDs. Moreover, this coupled ensemble exhibits decay properties of the spin polarization that vary with the excited spin density. This phenomenon can be quantitatively understood by considering interdot spin transfer into lower-energy levels of the surrounding QDs, where the transfer rate depends on the degree of state filling of each QD level. Published by AIP Publishing