1,374 research outputs found
On tadpoles and vacuum redefinitions in String Theory
Tadpoles accompany, in one form or another, all attempts to realize
supersymmetry breaking in String Theory, making the present constructions at
best incomplete. Whereas these tadpoles are typically large, a closer look at
the problem from a perturbative viewpoint has the potential of illuminating at
least some of its qualitative features in String Theory. A possible scheme to
this effect was proposed long ago by Fischler and Susskind, but incorporating
background redefinitions in string amplitudes in a systematic fashion has long
proved very difficult. In the first part of this paper, drawing from field
theory examples, we thus begin to explore what one can learn by working
perturbatively in a ``wrong'' vacuum. While unnatural in Field Theory, this
procedure presents evident advantages in String Theory, whose definition in
curved backgrounds is mostly beyond reach at the present time. At the field
theory level, we also identify and characterize some special choices of vacua
where tadpole resummations terminate after a few contributions. In the second
part we present a notable example where vacuum redefinitions can be dealt with
to some extent at the full string level, providing some evidence for a new link
between IIB and 0B orientifolds. We finally show that NS-NS tadpoles do not
manifest themselves to lowest order in certain classes of string constructions
with broken supersymmetry and parallel branes, including brane-antibrane pairs
and brane supersymmetry breaking models, that therefore have UV finite
threshold corrections at one loop.Comment: 51 pages, LaTeX, 7 eps figures. Typos corrected, refs added. Final
version to appear in Nucl. Phys. B. Thanks to W. Mueck for very interesting
correspondence. v3 was accidentally in draft forma
Identification alone versus intraoperative neuromonitoring of the recurrent laryngeal nerve during thyroid surgery: experience of 2034 consecutive patients
Background: The aim of this study was to evaluate the ability of intraoperative neuromonitoring in reducing the
postoperative recurrent laryngeal nerve palsy rate by a comparison between patients submitted to thyroidectomy
with intraoperative neuromonitoring and with routine identification alone.
Methods: Between June 2007 and December 2012, 2034 consecutive patients underwent thyroidectomy by a
single surgical team. We compared patients who have had neuromonitoring and patients who have undergone
surgery with nerve visualization alone. Patients in which neuromonitoring was not utilized (Group A) were 993,
patients in which was utilized (group B) were 1041.
Results: In group A 28 recurrent laryngeal nerve injuries were observed (2.82%), 21 (2.11%) transient and 7 (0.7%)
permanent. In group B 23 recurrent laryngeal nerve injuries were observed (2.21%), in 17 cases (1.63%) transient
and in 6 (0.58%) permanent. Differences were not statistically significative.
Conclusions: Visual nerve identification remains the gold standard of recurrent laryngeal nerve management in
thyroid surgery. Neuromonitoring helps to identify the nerve, in particular in difficult cases, but it did not decrease
nerve injuries compared with visualization alone. Future studies are warranted to evaluate the benefit of intraoperative
neuromonitoring in thyroidectomy, especially in conditions in which the recurrent nerve is at high risk of injury.
Keywords: Neuromonitoring, Recurrent laryngeal nerve, Thyroidectom
Follicular nodules (Thy3) of the thyroid: is total thyroidectomy the best option?
BACKGROUND: Identification of the best management strategy for nodules with Thy3 cytology presents particular problems for clinicians. This study investigates the ability of clinical, cytological and sonographic data to predict malignancy in indeterminate nodules with the scope of determining the need for total thyroidectomy in these patients. METHODS: The study population consisted of 249 cases presenting indeterminate nodules (Thy3): 198 females (79.5%) and 51 males (20.5%) with a mean age of 52.43 ± 13.68 years. All patients underwent total thyroidectomy. RESULTS: Malignancy was diagnosed in 87/249 patients (34.9%); thyroiditis co-existed in 119/249 cases (47.79%) and was associated with cancer in 40 cases (40/87; 45.98%). Of the sonographic characteristics, only echogenicity and the presence of irregular margins were identified as being statistically significant predictors of malignancy. 52/162 benign lesions (32.1%) and 54/87 malignant were hypoechoic (62.07%); irregular margins were present in 13/162 benign lesions (8.02%), and in 60/87 malignant lesions (68.97%). None of the clinical or cytological features, on the other hand, including age, gender, nodule size, the presence of microcalcifications or type 3 vascularization, were significantly associated with malignancy. CONCLUSIONS: The rate of malignancy in cytologically indeterminate lesions was high in the present study sample compared to other reported rates, and in a significant number of cases Hashimoto’s thyroiditis was also detected. Thus, considering the fact that clinical and cytological features were found to be inaccurate predictors of malignancy, it is our opinion that surgery should always be recommended. Moreover, total thyroidectomy is advisable, being the most suitable procedure in cases of multiple lesions, hyperplastic nodular goiter, or thyroiditis; the high incidence of malignancy and the unreliability of intraoperative frozen section examination also support this preference for total over hemi-thyroidectomy
On the traces of Hephaestus : skills, technology and social participation
In the general understanding, and also in scientific practice, technology and society are viewed as two distinct entities. Related to this view is the assumption that technology and human experience are quite different and unconnected and also the idea that modernity has uprooted, de-contextualized and disembodied technical rationality. Taking a contrary approach, this study represents a theoretical exploration aimed at showing that in the domain of technological development, there are significant margins for maneuver in which to recuperate and valorize human and social action. As a work of theoretical sociology or social epistemology, this thesis approaches its subject from the theoretical background of the philosophy and sociology of technique. The historical and conventional assumptions of this theoretical background, it is argued, have been and continue to be characterized by a hegemonically defined essentialist paradigm. This paradigm has been fiercely counteracted by two opposed approaches, critical theory and pragmatism. The present work combines these approaches, usually considered mutually incompatible, for the development of a new theoretical gaze or perspective. The aim has been to engage in a theoretical research oriented to a new philosophy of praxis in order to instigate a critical and constructivist approach to technology. The main result expected of this work is the provision of a problematized and multifaceted semantic map leading to a multidimensional conceptual re-integration of skilled experience in human technical action
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