297 research outputs found
Gauge protection in non-Abelian lattice gauge theories
Protection of gauge invariance in experimental realizations of lattice gauge
theories based on energy-penalty schemes has recently stimulated impressive
efforts both theoretically and in setups of quantum synthetic matter. A major
challenge is the reliability of such schemes in non-Abelian gauge theories
where local conservation laws do not commute. Here, we show through exact
diagonalization that non-Abelian gauge invariance can be reliably controlled
using gauge-protection terms that energetically stabilize the target gauge
sector in Hilbert space, suppressing gauge violations due to unitary
gauge-breaking errors. We present analytic arguments that predict a
volume-independent protection strength , which when sufficiently large leads
to the emergence of an \textit{adjusted} gauge theory with the same local gauge
symmetry up to least a timescale . Thereafter, a
\textit{renormalized} gauge theory dominates up to a timescale
with a volume-independent energy factor, similar
to the case of faulty Abelian gauge theories. Moreover, we show for certain
experimentally relevant errors that single-body protection terms robustly
suppress gauge violations up to all accessible evolution times in exact
diagonalization, and demonstrate that the adjusted gauge theory emerges in this
case as well. These single-body protection terms can be readily implemented
with fewer engineering requirements than the ideal gauge theory itself in
current ultracold-atom setups and NISQ devices.Comment: 24 pages, 7 figures, journal articl
Gauge-Symmetry Protection Using Single-Body Terms
Quantum-simulator hardware promises new insights into problems from particle
and nuclear physics. A major challenge is to reproduce gauge invariance, as
violations of this quintessential property of lattice gauge theories can have
dramatic consequences, e.g., the generation of a photon mass in quantum
electrodynamics. Here, we introduce an experimentally friendly method to
protect gauge invariance in lattice gauge theories against
coherent errors in a controllable way. Our method employs only single-body
energy-penalty terms, thus enabling practical implementations. As we derive
analytically, some sets of penalty coefficients render undesired gauge sectors
inaccessible by unitary dynamics for exponentially long times, and, for
few-body error terms, with resources independent of system size. These findings
constitute an exponential improvement over previously known results from
energy-gap protection or perturbative treatments. In our method, the
gauge-invariant subspace is protected by an emergent global symmetry, meaning
it can be immediately applied to other symmetries. In our numerical benchmarks
for continuous-time and digital quantum simulations, gauge protection holds for
all calculated evolution times (up to for continuous time, with
the relevant energy scale). Crucially, our gauge-protection technique is
simpler to realize than the associated ideal gauge theory, and can thus be
readily implemented in current ultracold-atom analog simulators as well as
digital noisy intermediate scale quantum (NISQ) devices.Comment: 19 pages, 12 figures, journal articl
Dynamical phase transitions in quantum spin models with antiferromagnetic long-range interactions
In recent years, dynamical phase transitions and out-of-equilibrium
criticality have been at the forefront of ultracold gases and condensed matter
research. Whereas universality and scaling are established topics in
equilibrium quantum many-body physics, out-of-equilibrium extensions of such
concepts still leave much to be desired. Using exact diagonalization and the
time-dependent variational principle in uniform martrix product states, we
calculate the time evolution of the local order parameter and Loschmidt return
rate in transverse-field Ising chains with antiferromagnetic power law-decaying
interactions, and map out the corresponding rich dynamical phase diagram.
\textit{Anomalous} cusps in the return rate, which are ubiquitous at small
quenches within the ordered phase in the case of ferromagnetic long-range
interactions, are absent within the accessible timescales of our simulations in
the antiferromagnetic case, showing that long-range interactions are not a
sufficient condition for their appearance. We attribute this to much weaker
domain-wall binding in the antiferromagnetic case. For quenches across the
quantum critical point, \textit{regular} cusps appear in the return rate and
connect to the local order parameter changing sign, indicating the concurrence
of two major concepts of dynamical phase transitions. Our results consolidate
conclusions of previous works that a necessary condition for the appearance of
anomalous cusps in the return rate after quenches within the ordered phase is
for topologically trivial local spin flips to be the energetically dominant
excitations in the spectrum of the quench Hamiltonian. Our findings are readily
accessible in modern trapped-ion setups, and we outline the associated
experimental considerations.Comment: Accepted version, 15 pages, 5 figure
Prospective, open, multi-centre phase I/II trial to assess safety and efficacy of neoadjuvant radiochemotherapy with docetaxel and oxaliplatin in patients with adenocarcinoma of the oesophagogastric junction
Background: This phase I/II-trial assessed the dose-limiting toxicities (DLT) and maximum tolerated dose (MTD) of neoadjuvant radiochemotherapy (RCT) with docetaxel and oxaliplatin in patients with locally advanced adenocarcinoma of the oesophagogastric junction.
Methods: Patients received neoadjuvant radiotherapy (50.4 Gy) together with weekly docetaxel (20 mg/m2 at dose level (DL) 1 and 2, 25 mg/m2 at DL 3) and oxaliplatin (40 mg/m2 at DL 1, 50 mg/m2 at DL 2 and 3) over 5 weeks. The primary endpoint was the DLT and the MTD of the RCT regimen. Secondary endpoints included overall response rate (ORR) and progression-free survival (PFS).
Results: A total of 24 patients were included. Four patients were treated at DL 1, 13 patients at DL 2 and 7 patients at DL 3. The MTD of the RCT was considered DL 2 with docetaxel 20 mg/m2 and oxaliplatin 50 mg/m2. Objective response (CR/PR) was observed in 32% (7/22) of patients. Eighteen patients (75%) underwent surgery after RCT. The median PFS for all patients (n = 24) was 6.5 months. The median overall survival for all patients (n = 24) was 16.3 months. Patients treated at DL 2 had a median overall survival of 29.5 months.
Conclusion: Neoadjuvant RCT with docetaxel 20 mg/m2 and oxaliplatin 50 mg/m2 was effective and showed a good toxicity profile. Future studies should consider the addition of targeted therapies to current neoadjuvant therapy regimens to further improve the outcome of patients with advanced cancer of the oesophagogastric junction.
Trial Registration: NCT0037498
Computer-assisted intraoperative 3D-navigation for liver surgery: a prospective randomized-controlled pilot study.
BACKGROUND
Liver surgery is the standard of care for primary and many secondary liver tumors. Due to variability and complexity in liver anatomy preoperative imaging is necessary to determine resectability and for planning the surgical strategy. In the last few years, computer-assisted resection planning has been introduced in liver surgery. Aim of this trial was the evaluation of computer-assisted three-dimensional (3D)-navigation for liver surgery.
METHODS
This study was a prospective randomized-controlled pilot trial and patients were randomized in navigated or non-navigated group. Primary end point was the quotient of intraoperative resected volume and planned resection volume. Secondary end points included operation time, resection margin and postoperative complications. 3D reconstructions were performed with MeVis Distant Services (MeVis AG, Bremen, Germany). The navigation system CAS-One Liver (CAScination AG, Bern, Switzerland) was used for intraoperative computer-assisted 3D-navigation.
RESULTS
The data of 16 patients with 20 liver tumors were used in this analysis. Of these, 8 liver tumors were resected with the utilization of intraoperative navigation. Two postoperative complications were classified grade IIIa or higher. There was no difference in duration of operation (189 vs. 180 min, P=0.970), rate of postoperative complications (n=1 vs. n=1, P=0.696) and length of hospital stay (9 vs. 7 days, P=0.368) between the two groups. Minimal resection margin (0.15 vs. 0.40 cm, P=0.384) and quotient of planned to intraoperative resection volume (0.94 vs. 1.11, P=0.305) were also similar.
CONCLUSIONS
Intraoperative navigation is a technology that can be safely used during liver resection. Surgical accuracy is not yet superior to the current standard of intraoperative orientation. Further technological advances with suitable deformation algorithms and augmented reality systems will enable a further improvement of the technical feasibility
Cesium and Strontium Contamination of Nuclear Plant Stainless Steel : Implications for Decommissioning and Waste Minimization
Stainless steels can become contaminated with radionuclides at nuclear sites. Their disposal as radioactive waste would be costly. If the nature of steel contamination could be understood, effective decontamination strategies could be designed and implemented during nuclear site decommissioning in an effort to release the steels from regulatory control. Here, batch uptake experiments have been used to understand Sr and Cs (fission product radionuclides) uptake onto AISI Type 304 stainless steel under conditions representative of spent nuclear fuel storage (alkaline ponds) and PUREX nuclear fuel reprocessing (HNO3). Solution (ICP-MS) and surface measurements (GD-OES depth profiling, TOF-SIMS, and XPS) and kinetic modeling of Sr and Cs removal from solution were used to characterize their uptake onto the steel and define the chemical composition and structure of the passive layer formed on the steel surfaces. Under passivating conditions (when the steel was exposed to solutions representative of alkaline ponds and 3 and 6 M HNO3), Sr and Cs were maintained at the steel surface by sorption/selective incorporation into the Cr-rich passive film. In 12 M HNO3, corrosion and severe intergranular attack led to Sr diffusion into the passive layer and steel bulk. In HNO3, Sr and Cs accumulation was also commensurate with corrosion product (Fe and Cr) readsorption, and in the 12 M HNO3 system, XPS documented the presence of Sr and Cs chromates.Peer reviewe
Diagnostik und Therapie von Lebermetastasen bei kolorektalem Primärtumor
Contrast-enhanced multislice computer tomography (MSCT) has established itself as the standard tomographic imaging method both for diagnosis and for treatment monitoring of hepatic lesions. To clarify local conditions before partial liver resection, diffusion-weighted magnetic resonance tomography (DWI-MRT) can also provide important additional information. In order to meet the criteria for a R0 resection, a margin of 0.5 mm seems to be sufficient. Neoadjuvant chemotherapy aiming to reduce tumour size can be given in parallel with portal artery embolisation without adversely affecting perioperative morbidity and mortality. As far as the management of primary resectable liver metastases is concerned, there is an urgent need for more studies. Despite the relatively limited evidence, adjuvant chemotherapy is currently more widely favoured in Germany than perioperative chemotherapy. There is also considerable need for studies concerning preoperative therapy in patients with liver metastases that are not (yet) resectable. In KRAS wild-type tumours, high response rates (in terms of a reduction in the size of metastases) are achieved with a cetuximab/chemotherapy combination. Bevacizumab/chemotherapy combinations lead to high rates of pathohistological complete and partial remissions. What the best parameter for judging the success of preoperative therapy is remains unknown, and so comparison studies using survival as a `hard' endpoint must be carried out
Spezielle Therapiesituationen beim metastasierten kolorektalen Karzinom
Specific Treatment Situations in Metastatic Colorectal Cancer As far as the management of primary resectable liver metastases is concerned, three approaches are currently competing with each other: surgery alone, surgery with pre- and postoperative chemotherapy, and surgery with postoperative chemotherapy alone. The core of the argument for pre- and postoperative chemotherapy in these patients is the European Organisation for Research and Treatment of Cancer (EORTC) 40983 study, which concluded that, in comparison with surgery alone, perioperative chemotherapy improved the 3-year progression-free survival (PFS) by 7 months. In contrast to this, there are two smaller studies - at a somewhat lower strength of evidence - indicating that adjuvant chemotherapy extends PFS by 9.1 months compared with surgery alone. In Germany, the adjuvant approach continues to be favored in many places; this can also be seen in the formulation of the S3 guideline. In patients with unresectable liver metastases - with the associated difficulty of classification due to the lack of clear and definitive criteria preoperative systemic therapy to induce `conversion' is indicated, in order to allow secondary resection. In KRAS wild-type tumors, high response rates ( in terms of a reduction in size of the metastases, such as according to RECIST ( Response Evaluation Criteria in Solid Tumors)) and a high conversion rate are achieved using a cetuximab/chemotherapy combination. Triple chemotherapy combinations with 5-fluorouracil (5-FU), oxaliplatin and irinotecan also produce high response rates. Bevacizumab/chemotherapy combinations have led to a high number of complete and partial pathohistological remissions in phase II studies; these seem to correlate with long survival times. In the absence of long-term survival data, it therefore seems to remain unclear as to what is the best parameter to use in order to assess the success of preoperative treatment. Lung metastases, too, or local peritoneal carcinomatosis can nowadays be operated on in selected patients with a good prospect of long-term remission or even cure. The surgery should, however, generally only be carried out in experienced centers, especially in the case of peritoneal carcinomatosis. For synchronous metastasization, the appropriate management depends on the size and extent of liver metastases and of the primary tumor. Small, peripherally lying and safely resectable liver metastases can be removed before or at the same time as the primary tumor, especially if a hemicolectomy is being carried out. If the metastases are unresectable and there is no bleeding or stenosis, the primary tumor can also be left in situ and systemic chemotherapy can be carried out first. However, it should be borne in mind that, according to current data, palliative resection of the primary tumor combined with systemic therapy leads to longer overall survival than does chemotherapy alone. Whether resection or chemotherapy should be done first therefore depends on the patient's clinical situation
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