Flat Bands and Chiral Optical Response of Moiré Insulators.

We present a low-energy model describing the reconstruction of the electronic spectrum in twisted bilayers of honeycomb crystals with broken sublattice symmetry. The resulting moiré patterns are classified into two families with different symmetry. In both cases, flat bands appear at relatively large angles without any magic-angle condition. Transitions between them give rise to sharp resonances in the optical absorption spectrum at frequencies well below the gap of the monolayer. Owing to their chiral symmetry, twisted bilayers display circular dichroism, that is, different absorption of left and right circularly polarized light. This optical activity is a nonlocal property determined by the stacking. In hexagonal boron nitride, sensitivity to the stacking leads to strikingly different circular dichroism in the two types of moirés. Our calculations exemplify how subtle properties of the electronic wave functions, encoded in current correlations between the layers, control physical observables of moiré materials.

Quantum spin Hall effect in two-dimensional crystals of transition-metal dichalcogenides.

We propose to engineer time-reversal-invariant topological insulators in two-dimensional crystals of transition-metal dichalcogenides (TMDCs). We note that, at low doping, semiconducting TMDCs under shear strain will develop spin-polarized Landau levels residing in different valleys. We argue that gaps between Landau levels in the range of 10-100 K are within experimental reach. In addition, we point out that a superlattice arising from a moiré pattern can lead to topologically nontrivial subbands. As a result, the edge transport becomes quantized, which can be probed in multiterminal devices made using strained 2D crystals and/or heterostructures. The strong d character of valence and conduction bands may also allow for the investigation of the effects of electron correlations on the topological phases.

Elliot-Yafet mechanism in graphene.

The differences between spin relaxation in graphene and in other materials are discussed. For relaxation by scattering processes, the Elliot-Yafet mechanism, the relation between the spin and the momentum scattering times, acquires a dependence on the carrier density, which is independent of the scattering mechanism and the relation between mobility and carrier concentration. This dependence puts severe restrictions on the origin of the spin relaxation in graphene. The density dependence of the spin relaxation allows us to distinguish between ordinary impurities and defects which modify locally the spin-orbit interaction.

Limits on charge carrier mobility in suspended graphene due to flexural phonons.

The temperature dependence of the mobility in suspended graphene samples is investigated. In clean samples, flexural phonons become the leading scattering mechanism at temperature T≳10 K, and the resistivity increases quadratically with T. Flexural phonons limit the intrinsic mobility down to a few m(2)/V s at room T. Their effect can be eliminated by applying strain or placing graphene on a substrate.

Economic costs associated with inadequate drug prescribing: an exploratory study in Chiapas, Mexico.

An exploratory study assessing the economic consequences of inadequate prescribing by health-care providers was carried out in two cities of Chiapas State, South Mexico. Two research methods were used: (a) an exit survey with pharmacy users (1190 interviews) and (b) in-depth individual interviews with patients at hospital level (19 interviews). For comparative purposes, three tracer conditions were selected: acute respiratory infection (ARI), diarrhoeal disease (DD) and hypertension. The main findings were that doctors, drug vendors at pharmacies, traditional healers, users of health-care services themselves (through self-prescription) and other health staff are all sources of inadequate prescribing and impose a substantial economic burden of unnecessary cost on health-care users. In general, treatment costs were high compared with standard treatments, and prescriptions included a high proportion of non-essential drugs (50-64%). Additional costs to the standard treatment were particularly high when the prescription was by a medical doctor (US$ 3.57 per ARI prescription and US$ 8.37 for DD). Losses attributable to inadequate prescribing averaged US$ 47 per patient. The study concludes that training programmes on rational drug use aimed exclusively at medical doctors can only have a limited effect in reducing economic losses due to inadequate prescribing. Such efforts should be extended to other providers who are very active in prescribing drugs and providing health advice. The main challenge that the Mexican health system will be facing in the foreseeable future is not only to improve equity of access to essential drugs, but also to improve quality of drug advice and prescription and rational use of drugs by the population.

[Akathisia secondary to tolcapone. Report of a case]. / Acatisia secundaria a tolcapone. Reporte de un caso.

The purpose of this work is to report a case of tolcapone-induced akathisia. A 39-year-old woman with Parkinson's disease, Hohen-Yahr IV, Webster 18 points with 10 years within onset, presented lack of clinical response to levodopa-carbidopa, pergolide, selegiline and trihexiphenidyl, showing freezing and wearing-off phenomena and choreic dyskinetic abnormal movements of the upper and lower extremities, during the six months previous to her evaluation. Her hepatic function was normal. Levodopa-carbidopa and selegiline were diminished to add tolcapone, as described elsewhere. During the first three weeks, the patient showed marked clinical improvement of previous complications and sustained improvement during 12.5 weeks. At the 13th week of tolcapone therapy the patient developed constant orofacial, trunk, and superior and lower limb ínvoluntary movements associated to lack of stand still. Laboratory tests showed discrete elevation of oxaloacetic-glutamic transminase, direct bilirrubin, indirect bilirubin, and alkaline phosphatase. Electroencephalogram and CT scan were normal. Tolcapone therapy was finished, and levodopa-carbidopa, pergolide and selegiline were diminished, procuring the disappearance of akathisia within 72 h.

Inadequate drug advice in the pharmacies of Guatemala and Mexico: the scale of the problem and explanatory factors.

A study of urban pharmacies in Guatemala and in Chiapas, southern Mexico, was undertaken to analyse the scale of the inadequate drug advice provided, and to identify the contributing factors. The estimate of the scale of the problem was based on the results of 969 approaches to 191 pharmacies by 'magic clients' (i.e. researchers pretending to be looking for treatment for relatives who had one of three 'tracer' diseases), interviews with 4469 pharmacy users as they left the same 191 pharmacies, and a comparison of the quality of advice offered by public and private pharmacies in Guatemala (based on exit interviews with 150 users). The contributing factors were explored using a provider survey (interviews with 166 pharmacy supervisors and 371 drug vendors), an in-depth study analysing large-chain and independent Mexican pharmacies, and a review of the national drug policies in both countries. Although only about 11% of all drug treatments were recommended in pharmacies (the rest being prescribed by physicians or recommended by kin-groups), this still represents large numbers of treatments. Overall, 501 individuals who visited the 191 study pharmacies over 2 days of observation received drugs recommended by pharmacy staff. Much of the pharmacy advice was revealed to be poor: > 80% of the treatments recommended to the 'magic clients' for diarrhoeal disease or acute respiratory infection included unnecessary or dangerous drugs. Few of those who worked in the pharmacies based their advice on careful case histories. Drug advice in pharmacies was much more likely to be of poor quality than that from physicians or even kin-groups. The factors behind this poor advice were identified as a lack of knowledge about standard treatments and legal regulations, incompetence among pharmacy staff, commercial pressures (particularly in the large-chain pharmacies of Mexico), and a failure to implement the existing regulations covering the drug market and its retail practices. It is recommended that: (1) pharmacy owners and drug vendors be made more aware that the selling of drugs should involve provision of healthcare (as well as reasonable profit-making); (2) existing drug-related legislation be reinforced (through consensus-building rather than coercion); and (3) mass training of pharmacy supervisors and drug vendors, in the standard treatment of common diseases, be undertaken. This process will be challenging and slow.