RESUMO
We study the interplay between Dirac and Schrödinger fermions in the polarization properties of a two-dimensional electron gas (2DEG). Specifically, we analyze the low-energy sector of narrow-gap semiconductors described by a two-band Kane model. In the context of quantum spin Hall insulators, particularly, in Hg(Cd)Te quantum wells, this model is named the Bernevig-Hughes-Zhang model. Interestingly, it describes electrons with intermediate properties between Dirac and Schrödinger fermions. We calculate the dynamical dielectric function of such a model at zero temperature within random phase approximation. Surprisingly, plasmon resonances are found in the intrinsic (undoped) limit, whereas they are absent-in that limit-in graphene as well as ordinary 2DEGs. Additionally, we demonstrate that the optical conductivity offers a quantitative way to identify the topological phase of Hg(Cd)Te quantum wells from a bulk measurement.
RESUMO
BACKGROUND: Gemcitabine and irinotecan have shown a broad range of activity in solid tumors, including small-cell lung cancer (SCLC), with a synergistic effect on SCLC cell lines. The objective of this phase II trial was to evaluate the activity of gemcitabine/irinotecan in patients with relapsed SCLC. PATIENTS AND METHODS: Thirty-five patients (15 with refractory disease and 20 with sensitive disease) who had experienced treatment failure with 1 previous chemotherapy regimen were recruited. Treatment consisted of gemcitabine 1,000 mg/m(2) and irinotecan 100 mg/m(2) on days 1 and 8 of a 21-day cycle for a maximum of 6 cycles. Eligibility criteria included an Eastern Cooperative Oncology Group performance status of 0-2, adequate organ function, and signed informed consent. RESULTS: All 35 patients were assessable for response, survival, and toxicity. Best objective responses exhibited were as follows: complete response in 2 patients (6%), partial response in 4 (11%; 95% confidence interval [CI], 21%-61%), stable disease in 7 (20%; 95% CI, 9%-45%), and progressive disease in 22 (63%; 95% CI, 17%-57%). Median time to disease progression was 3.4 months and median survival was 5.8 months. The 1-year survival rate was 34%. Toxicity was mainly hematologic. Grade 3/4 nausea and vomiting occurred in 9% of patients, neuropathy occurred in 2.8%, and diarrhea occurred in 14.3%. Survival was not significantly different for patients with refractory versus sensitive disease. CONCLUSION: The combination of gemcitabine/irinotecan was shown to be active as second-line chemotherapy, especially in patients with refractory disease.