Scaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer

Over the past 20 years, many efforts have been made to understand and control decoherence in 2D electron systems. In particular, several types of electronic interferometers have been considered in GaAs heterostructures, in order to protect the interfering electrons from decoherence. Nevertheless, it is now understood that several intrinsic decoherence sources fundamentally limit more advanced quantum manipulations. Here, we show that graphene offers a unique possibility to reach a regime where the decoherence is frozen and to study unexplored regimes of electron interferometry. We probe the decoherence of electron channels in a graphene quantum Hall PN junction, forming a Mach-Zehnder interferometer1,2, and unveil a scaling behavior of decay of the interference visibility with the temperature scaled by the interferometer length. It exhibits a remarkable crossover from an exponential decay at higher temperature to an algebraic decay at lower temperature where almost no decoherence occurs, a regime previously unobserved in GaAs interferometers.

Quantum Hall Valley Splitters and a Tunable Mach-Zehnder Interferometer in Graphene

Graphene is a very promising test bed for the field of electron quantum optics. However, a fully tunable and coherent electronic beam splitter is still missing. We report the demonstration of electronic beam splitters in graphene that couple quantum Hall edge channels having opposite valley polarizations. The electronic transmission of our beam splitters can be tuned from zero to near unity. By independently setting the beam splitters at the two corners of a graphene p-n junction to intermediate transmissions, we realize a fully tunable electronic Mach-Zehnder interferometer. This tunability allows us to unambiguously identify the quantum interferences due to the Mach-Zehnder interferometer, and to study their dependence with the beam-splitter transmission and the interferometer bias voltage. The comparison with conventional semiconductor interferometers points toward universal processes driving the quantum decoherence in those two different 2D systems, with graphene being much more robust to their effect.

[Difficulties encountered and solutions found when implementing stereotactic radiotherapy of non-small cell lung cancer]

The aim of this paper is to describe the difficulties encountered when implementing stereotactic radiotherapy of non-small cell lung cancer (T1-T2, N0, M0) using a voluntary breath-hold technique. From 25/03/2010 to 22/02/2011, eight patients with a non-small cell lung cancer were selected for treatment. CT images were obtained with the patient maintaining breath-hold using a spirometer. Treatment was delivered when the patient maintains this level of breath-hold. Treatment was performed with a 4 MV and 10 MV photon beams from a linear accelerator Varian 2100CS, equipped with a 120 leaves collimator. 60 Gy or 48 Gy were delivered, in four sessions, to the 80% isodose. The planning target volume (PTV) was defined by adding a 5mm margin to the internal target volume (ITV), the ITV corresponding to the gross tumour volume (GTV) plus a 3mm margin. CTV is considered equal to GTV. The non-understanding of the gating technique, the great number of beams and the limited breath-hold times led to the failure of some treatments. It can be explained by some patients insufficient respiratory abilities and the low dose rate of one of the beams used for treatment, thus forcing some radiation fields to be delivered in two or three times. Implementing such a technique can be limited by the patients' physical abilities and the materials used. Some solutions were found: a training phase more intense with a coaching of the breath-hold technique more precise, or the use of an abdominal compression device.

[Malignant gliomas]

Glial tumors represent 2000 to 3000 new cases per year in France and 75% of them are of high grade. Recent understanding of the molecular biology of these tumors revealed the importance of 1p19q codeletion and mgMT promotor methylation. Radiotherapy also recently evolved with the progress in medical imaging which allows a better definition of the target volumes. Even modest, therapeutic progress is based on chemoradiotherapy with temozolomide and on the development of non-coplanar conformational radiotherapy. Knowledge and precise evaluation of potential late effects of our treatments is necessary due to actual improvement of survival with chemoradiotherapy in glioblastoma.

[Management of Merkel cell carcinoma: Role of radiotherapy in elderly patients]

PURPOSE

Merkel cell carcinoma carcinoma (MCC) or primary cutaneous neuroendocrine carcinoma is a rare and aggressive malignancy affecting elderly. Optimal therapeutic strategy has not yet been established in elderly patients.

PATIENTS AND METHODS

From March 1996 to March 2007, 29 patients with Merkel cell carcinoma of were treated at the University Hospital of Amiens, France. Adjuvant radiotherapy (RT) was performed for 14 patients (50%) on the tumor bed with margins of 3 to 5cm, an average dose of 46Gy (30-60Gy), by 2Gy per fraction. Ten of them also received RT to the lymph node area at mean dose of 44.3Gy (26-50Gy). Duration of RT was 35 days. A retrospective analysis was conducted to better evaluate survival and prognostic factors.

RESULTS

Median overall survival (OS) was 18.9 months (3-122) and the median time to progression (MTP) 5.5 months (1-26). At 5 years, OS for irradiated patients was 47% (IC95: 12-82%) versus 27% (IC95: 5-49%) in cases of surgery alone (p=0.032). The most frequent sites of recurrence were nodal (34.5%), local (24.1%) and metastatic (17.2%). For patients over 70 years, eight (36.5%) were free of disease at last news, 8 (36.5%) had died from cancer and six from other causes (27%). In this subgroup, MTP was 6 months (2-19) and median OS of 19 months (4-87). There was no acute toxicity greater than grade 2.

CONCLUSION

Although limited by a retrospective analysis, this report suggests an advantage of postoperative RT for patients with MCC. It combined low toxicity and improvement of survival. Prospective multicenter trials are needed to clarify and validate the optimal strategy.

[The axial orientation of the phalanges following the curling up of the fingers]

This study follows and modestly completes those by Dubousset and Kapandji concerning the phenomena of axial (or longitudinal) rotation of the phalanges combined with flexion-extension of the fingers. Our analysis of the orientation of axial rotation of the skeletal elements of the digital chain, in relation to each other and during digito-palmar flexion was supported by simple observation, impressions in silicone paste, study of anatomical preparations, three-dimensional computed tomography. The index finger and middle finger tend to supinate. The ring finger undergoes virtually no rotation and the distal end of the little finger tends to pronate. These phenomena, essential for good adaptation to grip and fine manipulation must be taken into account by rehabilitation physicians when the amplitude of these movements are limited by immobilisation or disease.

Treatment of high-risk gestational trophoblastic disease with chemotherapy combinations containing cisplatin and etoposide

The authors have treated 22 patients with high-risk gestational trophoblastic disease (GTD) by cisplatin-etoposide-containing combinations. Sixteen patients were treated with dactinomycin, platinum, and etoposide combination (APE regimen) and six patients had platinum and etoposide combination (PE regimen). Fourteen patients were treated for resistant or relapsing GTD after first-line therapy, and eight patients initially. All 22 patients were high risk according to the World Health Organization prognostic score values. Sustained complete remission was achieved in 19 patients (86%). All eight patients who received treatment as initial therapy were cured (100%) whereas only 11 patients were cured among the 14 patients who failed prior chemotherapy (78%). Hematologic and renal toxicities were limited and no treatment-related deaths occurred in this group of patients. Cisplatin and etoposide could be more widely used in chemotherapeutic combinations for high-risk gestational trophoblastic disease.

[Venous drainage of Littler's neurovascular pedicle flap]

The antegrade transosseous injection of the digital veins, followed by dissection enables the authors to analyse the role of various networks in drainage of the pulp. The satellite veins of the digital artery in the finger are probably not involved. The venous return of the pulp is constituted by an anatomical continuity between the superficial palmar network and the common digital veins. A narrow anastomotic channel is demonstrated in the commissure between these two systems.