A modified nudged elastic band algorithm with adaptive spring lengths.

We present a modified version of the nudged elastic band (NEB) algorithm to find minimum energy paths connecting two known configurations. We show that replacing the harmonic band-energy term with a discretized version of the Onsager-Machlup action leads to a NEB algorithm with adaptive spring lengths that automatically increase the resolution of the minimum energy path around the saddle point of the potential energy surface. The method has the same computational cost per optimization step of the standard NEB algorithm and does not introduce additional parameters. We present applications to the isomerization of alanine dipeptide, the elimination of hydrogen from ethane, and the healing of a 5-77-5 defect in graphene.

Sliding friction of graphene/hexagonal -boron nitride heterojunctions: a route to robust superlubricity.

The origin of ultra-low friction exhibited by heterogeneous junctions of graphene and hexagonal boron nitride (h-BN) is revealed. For aligned interfaces, we identify a characteristic contact size, below which the junction behaves like its homogeneous counterparts with friction forces that grow linearly with the contact area. Superlubricity sets in due to the progressive appearance of Moiré patterns resulting in a collective stick-slip motion of the elevated super-structure ridges that turns into smooth soliton-like gliding with increasing contact size. Incommensurability effects are enhanced in misaligned contacts, where the friction coefficients further drop by orders of magnitude. Our fully atomistic simulations show that the superlubric regime in graphene/h-BN heterostructures persists up to significantly higher loads compared to the well-studied twisted homogeneous graphene interface. This indicates the potential of achieving robust superlubricity in practical applications using two-dimensional layered materials heterojunctions.

Treatment of typical amyelic somatic fractures with kyphoplasty and calcium phosphate cement: a critical analysis.

PURPOSE: Vertebroplasty and more recently kyphoplasty are recognized as techniques in the treatment of osteoporotic vertebral fractures and in case of pathological fracture like in secondary tumors. The recent introduction of calcium phosphate cement (CPC) that offers, at least theoretically, an osteointegrative capacity, absent in polymethyl methacrylate (PMMA), has generated interest for its use in the treatment of traumatic fractures (type A) even in young patients. METHODS: In this study, type A fractures without neurological signs were treated. A total of six male patients, of age between 21 and 55 years (mean age 38 years), were included. Fracture treatment was performed with kyphoplasty with balloon (Kyphon) and injection of calcium phosphate cement for a total of seven procedures. RESULTS: The results were evaluated according to the regional kyphosis angle and the local kyphosis angle. The postoperative X-ray control showed an average improvement of the regional kyphosis angle of 7.4°; however, this value was reduced by an average of 6.6° after 45 days with regard to the postoperative control. The local kyphosis angle showed an average improvement of 9° at the postoperative control with an average worsening of 9.2° in the control after 45 days. CONCLUSIONS: While kyphoplasty with the use of CPC in the treatment of type A traumatic fractures was effective in the treatment of pain, it has not been so far effective concerning the maintenance of the reduction obtained intra-operatively and its osteointegrative effect.

Surgical treatment of far lateral lumbar disc herniation. Identification of compressed root and discectomy by lateral approach.

STUDY DESIGN: A new method is described of compressed root identification and discectomy for extraforaminal disc herniation, by a lateral intertransversalis approach. OBJECTIVES: To describe a safe surgical approach that does not require resection of adjacent bone structures during extraforaminal discectomy. SUMMARY OF BACKGROUND DATA: Most earlier series have reported approaches that damaged bordering bone structures with wide laminoarthrectomy. This is an attempt at a safer, simpler surgical approach. METHODS: Thirteen patients with lateral hernia have undergone this surgical procedure since 1995. Herniectomy was performed after identification of the compressed root within the iliopsoas muscle. RESULTS: All the patients resumed the upright position with the aid of semirigid brace 24 hours after surgery. Upon awakening from the anesthesia, no patient reported peripheral pain. Motor deficits resolved after physical rehabilitation in all but one patient. At a mean follow-up of 14 months, there was no report of back pain. CONCLUSION: The procedure described in this article offers a simple alternative to the valid procedures presently at hand. It offers the advantage of no bone resection and of minimizing nerve structures manipulation.

Postlaminectomy cervical dislocation in von Recklinghausen's disease. A case report.

STUDY DESIGN: A case of a 9-year-old girl with von Recklinghausen's disease who has acute tetraparesis caused by a complete dislocation of C6-C7 after a cervical laminectomy performed at another hospital. OBJECTIVES: To demonstrate the treatment difficulties of cervical spine abnormality associated with neurofibromatosis. SUMMARY OF BACKGROUND DATA: Craig and Govender have reported cases of neurofibromatosis of the cervical spine (1992). METHODS: The patient underwent emergency surgery starting with a posterior release of the articular facets and with the positioning of two Roy-Camille plates. The dislocation of C6-C7 was reduced by an anterior approach. Finally the Roy-Camille plates were removed, a plate was implanted posteriorly at the C6 and C7 joints, and a posterior cable was positioned around the C2-C3 posterior arches. RESULTS: More than 4.5 years after surgery, the patient's neurologic condition remains satisfactory. She can walk and run and has no sphincter disorders. CONCLUSIONS: The results underline the importance of simultaneous anterior and posterior surgical approaches in this disease.

Relation between surgery-induced prolactin increase and the menstrual cycle phase at time of surgery in premenopausal breast cancer.

It has been suggested that both the menstrual cycle phase and postoperative changes in prolactin (PRL) secretion at the time of surgery may influence the prognosis of breast cancer. The present study was carried out to evaluate the relation between menstrual cycle period and surgery-induced PRL variations. We evaluated 32 premenopausal women with operable breast carcinoma; 17 were in perimenstrual phase (days 1-6 and 21-28) and 15 were in the mid-cycle (days 7-20) period at the time of surgery. To investigate serum levels of PRL, venous blood samples were collected before and 7 days after surgery. Postoperative hyperprolactinemia occurred in 17/32 patients and it was statistically more frequent in patients surgically treated during the perimenstrual phase than in the mid-cycle phase (12/17 vs 5/15; p less than 0.05), while no other parameter (including axillary node and estrogen receptor status) showed a significant influence on hyperprolactinemia rate. The results suggest that in premenopausal breast cancer patients surgery-induced hyperprolactinemia may be influenced by the menstrual cycle phase at the time of surgery.

Blood levels of IGF-I in non-small cell lung cancer: relation to clinical data.

Recent observations have demonstrated that somatomedins, mainly insulin-like growth factor-I (IGF-I), are growth factors for non-small cell lung cancer (NSCLC). On the basis of this evidence, a study was started to evaluate serum levels of IGF-I in a group of untreated NSCLC patients. The study included 46 patients, 25 of whom had an operable tumor, while the other 21 showed distant organ metastases. IGF-I and GH serum levels were measured by RIA in each patient; moreover, in operable patients, hormonal detections were made either before, or 7 days after surgery. The control group comprised 38 age-matched healthy subjects. Mean serum levels of IGF-I were significantly higher in cancer patients with respect to controls, while no difference was seen in mean GH values. Moreover, patients with metastases showed significantly higher levels of IGF-I than the patients without. Within the operable group, patients with lung adenocarcinoma had higher levels of IGF-I than those with epidermoid cell carcinoma, but this difference was not significant. Finally, no significant difference in IGF-I mean values was seen before and after surgical removal of tumors. This preliminary study shows that NSCLC patients may present abnormally high levels of IGF-I. Because of the stimulating role of IGF-I on NSCLC growth, this evidence could play a role in the clinical course of neoplastic lung disease.

Postoperative hyperprolactinaemia and early recurrence rate in breast cancer.

Serum levels of prolactin before and after surgery were measured in 90 women with breast cancer until the 5th postoperative month. Surgery-induced hyperprolactinaemia occurred in 51 patients, without significant correlation to any other clinical variable. After a median follow-up of 39 months, irrespective of each other variable (i.e. nodal involvement, oestrogen receptor status, adjuvant therapies), patients with postoperative hyperprolactinaemia had a significantly lower recurrence rate than those in whom surgery was not followed by an abnormal increase in prolactin secretion (3/51 vs. 13/39, P less than 0.001). These results suggest that, despite the stimulatory role of prolactin on mammary tumours, the lack of postoperative hyperprolactinaemia is an unfavourable prognostic factor because of its association with a higher relapse rate.