Finite curved creases in infinite isometric sheets

Geometric stress focusing, e.g. in a crumpled sheet, creates point-like vertices that terminate in a characteristic local crescent shape. The observed scaling of the size of this crescent is an open question in the stress focusing of elastic thin sheets. According to experiments and simulations, this size depends on the outer dimension of the sheet, but intuition and rudimentary energy balance indicate it should only depend on the sheet thickness. We address this discrepancy by modeling the observed crescent with a more geometric approach, where we treat the crescent as a curved crease in an isometric sheet. Although curved creases have already been studied extensively, the crescent in a crumpled sheet has its own unique features: the material crescent terminates within the material, and the material extent is indefinitely larger than the extent of the crescent. These features together with the general constraints of isometry lead to constraints linking the surface profile to the crease-line geometry. We construct several examples obeying these constraints, showing finite curved creases are fully realizable. This approach has some particular advantages over previous analyses, as we are able to describe the entire material without having to exclude the region around the sharp crescent. Finally, we deduce testable relations between the crease and the surrounding sheet, and discuss some of the implications of our approach with regards to the scaling of the crescent size.Comment: 15 pages, 7 figure

The design of public decision systems/ Mowitz

xiv, 162 hal ; 22 cm

Allergic contact dermatitis caused by dipropylene glycol diacrylate in the Omnipod® insulin pump

Background: Cases of allergic contact dermatitis (ACD) caused by isobornyl acrylate (IBOA) in the Omnipod® insulin pump have previously been reported. Objectives: To present three cases of patients with ACD caused by a new allergen in the pump, and results from chemical analyses. Methods: Omnipod pumps from different batches were analysed by gas chromatography–mass spectrometry. Aimed testing, with the department’s medical device (MD) series and substances identified in the pump including dipropylene glycol diacrylate (DPGDA) at 0·01% and 0·1% in petrolatum (pet.), was performed. Patch testing also included extracts from the device, the adhesive patch as is, and allergens from baseline series. Results: All patients tested positive to 0·1% DPGDA in pet., and two patients additionally to a 0·01% concentration. DPGDA was found in extracts of the Omnipod pumps brought by the patients. An Omnipod pump from an earlier batch contained tripropylene glycol diacrylate, IBOA, N,N-dimethylacrylamide, di(ethylene glycol)ethyl ether acrylate (DEGEA) but no DPGDA. One of the patients reacted positively to all of these allergens except DEGEA, which was not tested. Conclusions: When suspecting ACD to MDs, DPGDA at 0·1% in pet. should be tested. The contents of Omnipod have changed over time. Patch testing with updated test series and relevance assessment of positive reactions is a delicate task. Children, with lifelong use of MDs, risk contracting many allergies with potential cross-allergies. A question should be raised as to whether these low molecular weight acrylates should be used at all in devices constantly worn on the skin

Continuous glucose monitoring systems give contact dermatitis in children and adults despite efforts of providing less ‘allergy- prone’ devices : investigation and advice hampered by insufficient material for optimized patch test investigations

Background: Medical devices are increasingly being reported to cause contact allergic dermatitis reactions. Objective: Review of patients with diabetes type I referred for suspected allergic contact dermatitis to insulin pump or glucose sensor systems. Method: We have reviewed 11 referred diabetes mellitus patients investigated for allergic contact dermatitis reactions to medical devices and specifically Dexcom G6®. Extracts from the medical devices were analysed. Results: The majority of patients was children, the majority had relevant allergies and particularly allergy to isobornyl acrylate which was also found in the glucose sensor system Dexcom G6®. Conclusions: The following case reports bring in focus the fact that patients sensitized through use of one medical device and being advised the use of another, or find another product for a while useful, are not by necessity free from future episodes of allergic contact dermatitis. The case reports emphasize the need for collaboration since it is impossible for even well-equipped laboratories to properly investigate the medical devices when information on the substances used in production is not uniform and complete and material to investigate are scarce. The importance of adequate patch test series and testing with own material and furthermore the importance to re-analyse medical devices and re-analyse test data are emphasized

Occupational Contact Dermatitis-Thoughts on Establishing of Contact Allergy to Products Containing Well Known as Well as Initially Unidentified Sensitizers

Occupational dermatosis are common all over the world. The prevalence depends on many factors including whether the legal system acknowledges both causation and aggravation of occupational dermatosis

Contact dermatitis from glucose sensors in Spain: A multicentric approach

Background: Allergic contact dermatitis from glucose sensors may interfere with their ongoing application. Objective: To evaluate a series of Spanish patients with contact dermatitis to glucose sensors regarding former sources of contact allergens, patch test results, and outcomes from the ongoing use of the device. Methods: A series of patients with contact dermatitis from glucose sensors was investigated in eight dermatology departments across Spain (epidemiological features, brands, latency time to develop dermatitis, the ability to continue using the devices as well as the patch test results). Results: Thirty patients were evaluated (mean age 20.9 years). A total of 66.7% were children and 66.7% female. Ninety per cent used Freestyle Libre (FSL). Eight of 26 (30.8%) reacted to isobornyl acrylate (IBOA) and two of 20 (10.0%) to N,N dimethylacrylamide (DMAA). The mean latency time to develop dermatitis was 9 months. Sixteen of 29 (55.2%) patients continued using the same sensor causing the reaction. Thirteen of 29 (44.8%) patients were unable to continue using the sensor because of severe reactions. Of these, five were positive to IBOA, one to IBOA and DMAA, one to DMAA, one to colophony, and one to isopropyl alcohol wipes. In one patient, the outcome was unknown. Conclusion: The frequency of sensitisation to IBOA and DMAA, was lower than in other European series, but similar to a previously published Spanish article. Legislation requiring manufacturers to provide information regarding the composition of medical devices and cooperate with the investigations into contact dermatitis is urgently needed