Sparse and stable Markowitz portfolios

We consider the problem of portfolio selection within the classical Markowitz mean-variance framework, reformulated as a constrained least-squares regression problem. We propose to add to the objective function a penalty proportional to the sum of the absolute values of the portfolio weights. This penalty regularizes (stabilizes) the optimization problem, encourages sparse portfolios (i.e. portfolios with only few active positions), and allows to account for transaction costs. Our approach recovers as special cases the no-short-positions portfolios, but does allow for short positions in limited number. We implement this methodology on two benchmark data sets constructed by Fama and French. Using only a modest amount of training data, we construct portfolios whose out-of-sample performance, as measured by Sharpe ratio, is consistently and significantly better than that of the naive evenly-weighted portfolio which constitutes, as shown in recent literature, a very tough benchmark.Comment: Better emphasis of main result, new abstract, new examples and figures. New appendix with full details of algorithm. 17 pages, 6 figure

Are we overusing IVF?

Peer reviewedPublisher PD

A rapid procedure for the extraction of genomic DNA from intact Aspergillus spores

Genomic DNA of different species of Aspergillus was prepared from intact spores using the Nucleon MiY kit of Amersham. The method is rapid, does not involve mechanical disruption of the spores nor the use of phenol-chloroform extractions and yields DNA that is suitable for PCR amplification and Southern analysis. The method is also applicable to mycelium ground with glass beads

On difference and doubt as tools for critical engagement with public health

This paper argues that critical public health should reengage with public health as practice by drawing on versions of Science and Technology Studies (STS) that ‘de-centre the human’ and by seeking alternative forms of critique to work inspired by Foucault. Based on close reading of work by Annemarie Mol, John Law, Vicky Singleton and others, I demonstrate that these authors pursue a conversation with Foucault but suggest new approaches to studying contemporary public health work in different settings. Proposing that we ‘doubt’ both the unity of public health and its effects, I argue that this version of STS opens up a space to recognise multiplicity; to avoid idealising what is being criticised; and to celebrate or care for public health practices as part of critique. Finally I oppose the view that considering technologies, materials and microbes leads to micro-level analysis or political neutrality, and suggest that it allows us to reframe studies of public health to account for inequalities and to draw attention to weak or retreating states, active markets and the entangled relations of humans and non-humans across the world

THE USE OF VIRTUAL REALITY AS AN INFORMATION TOOL ON EXTERNALITIES OF ENERGY SOURCES

Almost daily communication vehicles make some reference to the need to combat the indiscriminated use of fossil fuels and to use less polluting energy sources. In this scenario, nuclear energy should be presented as an option but this is still covered by many myths. Thus, to inform the youth public about the characteristics of the main sources that compose the brazilian energy matrix it is necessary to promote the transfer of knowledge and to demystify the nuclear sector in playful and responsible way

Efficacy of lateral eyelid-block excision with canthoplasty and full-thickness skin grafting in lower eyelid cicatricial ectropion

Purpose: To report on the outcomes of our preferred surgical technique for the correction of lower eyelid cicatricial ectropion. Methods: We conducted a retrospective, nonrandomized, interventional analysis of a consecutive case series of patients with cicatricial lower lid ectropion treated with adhesiolysis, lateral eyelid-block excision with canthoplasty and full-thickness skin grafting. Donor sites included the ipsi- or contralateral upper eyelid and pre- or retroauricular skin. All patients were treated by one of our oculoplastic surgeons in the period from January 2005 to January 2017 in the Rotterdam Eye Hospital/Focus Clinic Rotterdam. We assessed postoperative lower eyelid apposition, the occurrence of intra- and postoperative complications and the reoperation rate. Results: We included 38 eyelids of 32 patients, of whom 17 were male and 15 were female. The minimal postoperative follow-up was 3 months. A total of 27 of 38 eyelids showed good postoperative apposition. Skin graft donor sites were the ipsi- or contralateral upper eyelid (47% and 16%, respectively) and the pre- or retroauricular skin (26% and 11%, respectively). No intraoperative complications occurred, but one patient developed a transient allergic contact dermatitis in the early postoperative phase. Two of 38 eyelids (two of 32 patients) required another surgical intervention (block excision) for residual or recurrent ectropion, with favourable outcomes. There was 100% viability of the skin grafts. Conclusion: Repair of lower eyelid ectropion with lateral block excision, canthoplasty and full-thickness skin grafting is an effective procedure with minimal donor site morbidity, excellent graft survival rates and a low reoperation rate

Qualitative aspects and validation of a screening method for pesticides in vegetables and fruits based on liquid chromatography coupled to full scan high resolution (Orbitrap) mass spectrometry

The analytical capabilities of liquid chromatography with single-stage high-resolution mass spectrometry have been investigated with emphasis on qualitative aspects related to selective detection during screening and to identification. The study involved 21 different vegetable and fruit commodities, a screening database of 556 pesticides for evaluation of false positives, and a test set of 130 pesticides spiked to the commodities at 0.01, 0.05, and 0.20 mg/kg for evaluation of false negatives. The final method involved a QuEChERS-based sample preparation (without dSPE clean up) and full scan acquisition using alternating scan events without/with fragmentation, at a resolving power of 50,000. Analyte detection was based on extraction of the exact mass (±5 ppm) of the major adduct ion at the database retention time ±30 s and the presence of a second diagnostic ion. Various options for the additional ion were investigated and compared (other adduct ions, M + 1 or M + 2 isotopes, fragments). The two-ion approach for selective detection of the pesticides in the full scan data was compared with two alternative approaches based on response thresholds. Using the two-ion approach, the number of false positives out of 11,676 pesticide/commodity combinations targeted was 36 (0.3 %). The percentage of false negatives, assessed for 2,730 pesticide/commodity combinations, was 13 %, 3 %, and 1 % at the 0.01-, 0.05-, and 0.20-mg/kg level, respectively (slightly higher with fully automated detection). Following the SANCO/12495/2011 protocol for validation of screening methods, the screening detection limit was determined for 130 pesticides and found to be 0.01, 0.05, and ≥0.20 mg/kg for 86, 30, and 14 pesticides, respectively. For the detected pesticides in the spiked samples, the ability for unambiguous identification according to EU criteria was evaluated. A proposal for adaption of the criteria was made