M. A. Seo

Fourier-transform terahertz near-field imaging of one-dimensional slit arrays: mapping of electric-field-, magnetic-field-, and Poynting vectors

We present 2D measurements of the full THz electric field behind a sample consisting of multiple slits in a metal foil. Our measurements, which have a sub-wavelength spatial, and a sub-period temporal resolution, reveal electric field lines, electric field vortices and saddle points. From our measurements we are able to reconstruct the magnetic field and, finally, the position and time-dependent Poynting vector which shows the flow of energy behind the sample. Our results show that it is possible to study the flow of light near sub-wavelength plasmonic structures such as slit-arrays and, by implication, other metamaterial samples.

Advanced terahertz electric near-field measurements at sub-wavelength diameter metallic apertures

Using terahertz-light excitation, we have measured with sub-wavelength spatial, and sub-cycle temporal resolution the time- and frequency-dependent electric-field and surface-charge density in the vicinity of small metallic holes. In addition to a singularity like concentration of the electric field near the hole edges, we observe, that holes can act as differential operators whose near-field output is the time-derivative of the incident electric field. Our results confirm the well-known predictions made by Bouwkamp, Philips Res. Rep. 5, 321-332 (1950), and reveal, with unprecedented detail, what physically happens when light passes through a small hole.

Near field imaging of terahertz focusing onto rectangular apertures

We performed terahertz near-field experiments on single rectangular holes with various lengths grown on an electro-optic crystal substrate with lambda/100 resolution. We find that the near-field amplitude becomes proportionally larger as the rectangle becomes narrower, strongly suggesting that a constant energy passes through even for a very narrow slit. The occurrence of a large field enhancement at the fundamental localized resonance is discussed confirming the funneling of energy at the near-field.

Terahertz nanoresonators: Giant field enhancement and ultrabroadband performance

Transmission of terahertz (THz) electromagnetic waves through a series of nanoresonator arrays punctured in a thin metallic film is investigated. Over 30% of normalized transmitted amplitude is observed with only 0.18% of aperture-coverage, implying an electric field enhancement of 170. Increasing the coverage to 0.6% results in a 90% normalized amplitude, with a broader line width. Inspired by log-periodic antenna, we put ten nanoresonators with four different lengths per unit cell, succeeding in an ultrabroadband THz filter with one decade width between 0.2 and 2.0 THz.

Palliative chemotherapy for patients with recurrent hepatocellular carcinoma after liver transplantation

Background and Aim:  The majority of patients with post‐transplantation recurrence of hepatocellular carcinoma (HCC) have extrahepatic metastases and multifocal lesions. Therefore, they have few treatment options and may not be amenable for local therapy. The safety and efficacy of palliative chemotherapy in this population has not been reported.

Irinotecan Combined with 5-Fluorouracil and Leucovorin as Second-line Chemotherapy for Metastatic or Relapsed Gastric Cancer

OBJECTIVE We analysed the efficacy and toxicity of irinotecan, leucovorin and 5-fluorouracil (FOLFIRI) chemotherapy as second-line treatment for metastatic or relapsed gastric cancer (MRGC) in a clinical practice setting. Factors to select patients who may benefit from salvage chemotherapy was also analysed. METHODS Patients with MRGC with progression on or within 6 months after discontinuing platinum-based chemotherapy received FOLFIRI as second-line therapy. The FOLFIRI regimen consisted of irinotecan (180 mg/m(2); day 1) combined with leucovorin (200 mg/m(2)), followed by 5-fluorouracil (400 mg/m(2)) as a bolus and 600 mg/m(2) as a 22-h infusion on days 1 and 2 every 2 weeks. RESULTS Fifty-one patients received a total of 282 courses of chemotherapy. No patients had complete remission (CR), but 9 patients achieved partial remission (PR). Stable disease (SD) was documented in 15 patients. The median progression-free survival (PFS) and overall survival (OS) were 3.2 and 9.1 months, respectively. Toxicities were tolerable and grade 3/4 neutropenia was observed in 49 cycles (17%). In multivariate analysis, patients with less organ involvement by metastasis and good performance status (PS) were independently associated with a longer PFS and OS (P < 0.05). Disease control (CR, PR or SD) after first-line chemotherapy were related to a longer PFS (P = 0.02), but had no effect on OS. CONCLUSIONS FOLFIRI was tolerable and showed modest activity as a second-line therapy in MRGC. Less organ involvement by metastasis or good PS may be optimal selection criteria for patients with MRGC who are suitable for second-line chemotherapy.

Dielectric constant engineering with polymethylmethacrylate-graphite metastate composites in the terahertz region

A method for manufacturing terahertz absorber is presented. Varying fractions of graphite powder are mixed with the host poly methylmethacrylate powder and compress molded. The shielding efficiency, together with real and imaginary parts of the dielectric constant, is unambiguously determined by terahertz time domain spectroscopy in the continuous frequency range of 0.1–1.6THz. While the composites are absorptive in most of the frequency range with relatively small reflection, it turns metallic at a high enough graphite fraction of 35.7%: there exists a zero crossing of the real part of dielectric function er(ω) to negative values below 0.22THz. Our method provides an easy-to-control way of manufacturing terahertz absorbers with a wide range of shielding efficiency and low reflectance.

Resonance behavior of single ultrathin slot antennas on finite dielectric substrates in terahertz regime

We investigate resonance behaviors of optically thin metallic slot antennas on finite substrates in terahertz frequency regime. By carefully analyzing theoretical and experimental results, we observe that slot antennas fabricated in a gold film with a thickness below the skin depth of gold show blueshifted resonance frequencies for the increasing slot width, while the opposite resonance behaviors appear when the slot antennas are perforated in perfectly electric conductor. In addition, we find that for slot antenna sustained by a finite substrate its thickness and the slot width are additional crucial factors determining the resonance frequency of slot antennas.

Polarization dependent transmission through asymmetric C-shaped holes

We report that asymmetric c-shaped holes show mode switching between single- and double-resonance frequencies in the terahertz region, when the polarization direction of the incident light is controlled. The number of resonant frequencies is attributed to fundamental shape modes such as circle-, coaxial-, and rectangular-shaped holes activated under each polarization condition. All of these resonant peaks also show a transmission of over 90% with the assistance of the periodically arranged holes. These experimental results are in close agreement with theoretical simulations.

Patterns of palliative procedures and clinical outcomes in patients with advanced non-small cell lung cancer

BACKGROUND Despite recent progress in palliative chemotherapy for advanced non-small cell lung cancer (NSCLC), the prognosis is still poor. Aside from multiple lines of chemotherapy, many patients need palliative procedures due to disease-related events. The patterns of events requiring palliative procedures and their impact on the clinical course have not been well described. METHODS We evaluated 162 patients who were diagnosed with stage IIIB (with malignant effusion) or IV NSCLC at Seoul National University Hospital in 2005. The patterns of disease-related events requiring palliative procedures, the palliative procedures given, and the clinical outcomes were retrospectively analyzed. RESULTS Of the 162 patients, 107 were male (66%) and 55 were female (34%) with a median age of 61 years (range 31-90). Among these patients, 108 patients (66%) received palliative procedures due to disease-related events. Forty-nine patients (30%) needed a palliative procedure at the time of diagnosis, and 59 patients (36%) required palliative procedure later during the course of their treatment. The events requiring palliative procedures were thoracic events (malignant effusion or severe pneumonia requiring intensive care unit care not related to treatment) in 32 (30%), CNS events (brain metastasis or leptomeningeal metastasis) in 37 (34%), skeletal events (bone metastasis requiring radiation, spinal cord compression, hypercalcemia) in 29 (27%), and other events in 10 (9%). The patients who had events at the time of diagnosis showed comparable overall survival to the patients without events at the time of diagnosis (14.6 months vs. 13.3 months, p=0.65). The patients with later events during their course of treatment had a short median survival after the event requiring palliative procedures (median 2.7 months, 95% CI 2.19-3.21). CONCLUSION A considerable proportion of patients with advanced NSCLC receive palliative procedures apart from chemotherapy. These interventions should be taken into consideration for comprehensive cancer care and timely cooperation with palliative care team.