Scale invariance and universality of force networks in static granular matter

Force networks form the skeleton of static granular matter. They are the key ingredient to mechanical properties, such as stability, elasticity and sound transmission, which are of utmost importance for civil engineering and industrial processing. Previous studies have focused on the global structure of external forces (the boundary condition), and on the probability distribution of individual contact forces. The disordered spatial structure of the force network, however, has remained elusive so far. Here we report evidence for scale invariance of clusters of particles that interact via relatively strong forces. We analyzed granular packings generated by molecular dynamics simulations mimicking real granular matter; despite the visual variation, force networks for various values of the confining pressure and other parameters have identical scaling exponents and scaling function, and thus determine a universality class. Remarkably, the flat ensemble of force configurations--a simple generalization of equilibrium statistical mechanics--belongs to the same universality class, while some widely studied simplified models do not.Comment: 15 pages, 4 figures; to appear in Natur

Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after photorefractive keratectomy in high myopia: a prospective clinical study

BACKGROUND: To study the effect of prophylactic application of mitomycin-C on haze formation in photorefractive keratectomy (PRK) for high myopia. METHODS: Fifty-four eyes of 28 myopic patients were enrolled in this prospective study. All eyes were operated by PRK followed by 0.02% mitomycin-C application for two minutes and washed with 20 ml normal saline afterwards. All eyes were examined thoroughly on the first 7 days and one month after surgery; 48 eyes (88.9%) at 3 and 6 months postoperatively. Hanna grading (in the scale of 0 to 4+) was used for assessment of corneal haze. RESULTS: The mean spherical equivalent refraction (SE) was -7.08 diopters (D) ± 1.11 (SD) preoperatively. Six months after surgery, 37 eyes (77.1%) achieved an uncorrected visual acuity (UCVA) of 20/20 or better, all eyes had a UCVA of 20/40 or better and 45 (93.7%) eyes had an SE within ± 1.00D. One month postoperatively, 2 eyes (3.7%) had grade 0.5+ of haze, while at 3 and 6 months after surgery no visited eye had haze at all. All eyes had a best corrected visual acuity (BCVA) of 20/40 or better and there were no lost lines in BCVA by 6 months after surgery. In spatial frequencies of 6 and 12 cycles per degree contrast sensitivity had decreased immediately after PRK and it had increased 1.5 lines by the 6(th )postoperative month compared to the preoperative data. CONCLUSIONS: The results show the efficacy of mitomycin-C in preventing corneal haze after treatment of high myopia with PRK. This method- PRK + mitomycin-C – can be considered an alternative treatment for myopic patients whose corneal thicknesses are inadequate for laser in situ keratomileusis (LASIK). However, the results should be confirmed in longer follow-ups

Safety of besifloxacin ophthalmic suspension 0.6% in refractive surgery: a retrospective chart review of post-LASIK patients

CorrigendumNielsen SA, McDonald MB, Majmudar PA. Safety of besifloxacin ophthalmic suspension 0.6% in refractive surgery: a retrospective chart review of post-LASIK patients. Clinical Ophthalmology. 2013;7:149–156. The paper titled "Safety of besifloxacin ophthalmic suspension 0.6% in refractive surgery: a retrospective chart review of post-LASIK patients," contains an inaccurate description of the intraoperative use of medications.In the Results section it is reported that 31.8% (170/534) of besifloxacin cases and 97.0% (259/267) of moxifloxacin cases had drops applied directly to the flap interface. We have determined that ambiguity in the design of the electronic case report form resulted in all day-of-surgery drops provided to patients in the LASER suite being reported in the flap interface field. The authors have since clarified with each surgeon who reported intraoperative drug use that the drops were delivered either prior to the flap creation, or following replacement of the flap.The sentence at the top of page 152 stating: "Of note, 31.8% (170/534) of besifloxacin cases and 97.0% (259/267) of moxifloxacin cases had drops applied directly to the flap interface" should say: "Of note, 31.8% (170/534) of besifloxacin cases and 97.0% (259/267) of moxifloxacin cases had intraoperative drops applied."Read the original articl

The Prospective Health Assessment of Cataract Patients’ Ocular Surface (PHACO) study: the effect of dry eye

William B Trattler,1 Parag A Majmudar,2 Eric D Donnenfeld,3 Marguerite B McDonald,4 Karl G Stonecipher,5 Damien F Goldberg6 On behalf of the PHACO Study Group 1Center for Excellence in Eye Care, Miami, FL, USA; 2Chicago Cornea Consultants, Chicago, IL, USA; 3Ophthalmic Consultants of Long Island, Garden City, NY, USA; 4Ophthalmic Consultants of Long Island, Lynbrook, NY, USA; 5University North Carolina School of Medicine, Chapel Hill, NC, USA; 6Wolstan & Goldberg Eye Associates, Torrance, CA, USA Purpose: To determine the incidence and severity of dry eye as determined by the International Task Force (ITF) scale in patients being screened for cataract surgery.Patients and methods: This was a prospective, multi-center, observational study of 136 patients, at least 55 years of age, who were scheduled to undergo cataract surgery. The primary outcome measure was the incidence of dry eye as evaluated by grade on the ITF scale and secondary outcome measures include tear break-up time (TBUT), ocular surface disease index score, corneal staining with fluorescein, conjunctival staining with lissamine green, and a patient questionnaire to evaluate symptoms of dry eye.Results: Mean patient age was 70.7 years. A total of 73.5% of patients were Caucasian and 50% were female. Almost 60% had never complained of a foreign body sensation; only 13% complained of a foreign body sensation half or most of the time. The majority of patients (62.9%) had a TBUT ≤5 seconds, 77% of eyes had positive corneal staining and 50% of the eyes had positive central corneal staining. Eighteen percent had Schirmer’s score with anesthesia ≤5 mm.Conclusion: The incidence of dry eye in patients scheduled to undergo cataract surgery in a real-world setting is higher than anticipated. Keywords: cataract surgery screening, dry eye, International Task Force scale, observational stud