Decoding Van der Waals Impact on Chirality Transfer in Perovskite Structures: Density Functional Theory Insights.

Chiral organic-inorganic perovskites exhibit unique physicochemical properties driven by the symmetry of monovalent organic cations. However, an atomistic understanding of how chiral cations transfer their chirality to the inorganic framework and the role played by van der Waals (vdW) interactions in this process is still incomplete. In this work, we report a theoretical investigation, based on density functional theory calculations within the Perdew-Burke-Ernzerhof (PBE) formulation for the exchange-correlation functional, into the role of the vdW interactions in the chirality transfer process. For that, we selected several vdW corrections, namely, Grimme (D2, D3, D3(BJ)), Tkatchenko-Scheffler (TS, TS+SCS, TS+HSI), density-dependent energy correction (dDsC), and many-body scattering (MBD) energy method correction. For the chiral perovskite systems, we selected a set of chiral organic-inorganic perovskites with several dimensions, namely, from zero-dimensional to three-dimensional, each having enantiomers with R and S configurations. Based on a statistical treatment of the relative errors of all lattice parameters with respect to experimental data, we found that D3, D3(BJ), TS, TS+SCS, TS+HSI, and MBD vdW are the most accurate corrections to describe the equilibrium structural properties of chiral perovskites using the PBE method. We identify chirality-induced sequential asymmetries of distorted octahedrons and propose angular descriptors to quantify them, where the orientations of these distortions depend on the R or S nature of the chiral cations. Furthermore, we demonstrate the importance of accurate vdW interactions in precisely describing these asymmetric distortions. By means of binding energies and charge-transfer analysis, we show that the impact of vdW corrections on the charge distribution leads to a subtle strengthening of hydrogen bonds between chiral cations and inorganic octahedra, resulting in an increase in the binding energy. Finally, we identified that the Rashba-Dresselhaus effect in two-dimensionality is refined by vdW interactions.

Atomic-scale insights in the interplay of chemical composition and chirality in two-dimensional chiral perovskites.

The incorporation of chiral molecules (A) in materials based on hybrid ABX3 perovskites has opened new paths to tune the optoelectronic properties of perovskites through the transfer of chirality to the inorganic BX framework. However, our atomistic understanding of the role of chemical BX composition in the magnitude of the chirality transfer is far from complete. In this study, we use density functional theory calculations and the experimental Ruddlesden-Popper chiral (R-/S-NEA)2PbBr4 structure (R-/S-NEA = R-/S-1-(1-naphthyl)ethylammonium) to investigate the effects induced by chemical substitution of Pb by Ge or Sn and Br by Cl or I on the transfer of chirality and physical-chemical properties. We have observed that different enantiomers result in opposing orientations of octahedral tiltings within the inorganic framework, thus transferring chirality to the inorganic structure. The tilts are greater in perovskites based on Pb and decrease in the sequence of Cl to Br to I, as a consequence of the decrease in the halide electronegativity that weakens the interactions between X and the -N+H3 group of the NEA chiral cation. The chirality transfer is also evident in the Rashba-Dresselhaus effects on the electronic band structure, in which we found magnitudes directly correlated to the trends of octahedra tilting. The band offsets of substitutions B and X are predominantly influenced by their natural atomic energy levels, while organic molecules play a pivotal role in modulating the ionic potential and electron affinity in systems containing light atoms. The band gap values range from 1.91 up to 3.77 eV, with chirality and anion electronegativity providing significant tuning effects on whether the band gaps are direct or indirect.

Time in range and HbA1C after 6 months with a multidisciplinary program for children and adolescents with diabetes mellitus, real world data from Mexico City.

BACKGROUND: Multidisciplinary interventions may be useful for children and adolescents with diabetes mellitus (DM), especially in areas where new blood glucose monitoring and control technologies are difficult to access. METHODS: PAANDA, a care program for adolescents and children with diabetes, was implemented in patients aged 0 to 18 years and 11 months. The effect of the intervention was determined by self-blood glucose monitoring (SBGM) and glycosylated hemoglobin (HbA1C ) levels at start and after 6 months. RESULTS: A total of 121 patients with DM were evaluated, mean age of 14.27 years (SD: 4.60 years). Blood glucose measurements in range (70-120 mg/dL pre-prandial or 70-180 mg/dL post-prandial) increased by 20.67% before breakfast, 8.14% after breakfast (both P-value <.001), 5.02% before lunch (P-value = .02), 8.66% after lunch (P-value <.001), 11.50% before dinner (P-value <.001), 11.87% after dinner (P-value <.001), and 8.00% at dawn (P-value = .001). This change was accompanied by fewer values in the hyperglycemic category (-19.49% before breakfast, -7.73% after breakfast, both P-value <.001) and hypoglycemia (-1.18%). HbA1C levels decreased significantly 1.8% (P-value = .018). Multivariate logistic regression analysis showed an increase in glycemic control associated with each month after the intervention time in the PAANDA program (P-value <.001 for all the time points evaluated) and a significant decrease in glycemic variability. CONCLUSIONS: The multidisciplinary PAANDA intervention had a beneficial effect on glycemic control, with an improved time in range in a population of children and adolescents with DM.

Association of preoperative spinal drain placement with spinal cord ischemia among patients undergoing thoracic and thoracoabdominal endovascular aortic repair.

OBJECTIVE: Spinal cord ischemia (SCI) is among the most devastating complications of thoracic endovascular aortic repair (TEVAR). Spinal fluid drainage has been proposed as a viable means to reduce SCI, but few data exist to support its routine use. This study investigated the association of preoperative spinal fluid drainage with the risk of SCI after TEVAR. METHODS: The Vascular Quality Initiative TEVAR module was queried for adult patients (≥18 years) undergoing TEVAR (coverage of zones 0-5) between September 2014 and March 2018 (inclusive). Patients with preoperative spinal malperfusion, aortic rupture on presentation, and connective tissue disorders were excluded. One-to-one propensity matching was used to balance patients on 44 separate dimensions by the nearest neighbor principle to compare those with vs those without preoperative spinal drainage. The primary end point was SCI still present at the time of discharge. Secondary outcomes were 30-day mortality and prolonged intensive care unit stay (>7 days). RESULTS: Among 4287 patients who underwent TEVAR (mean age, 67.1 [standard deviation, 13.7] years; 1665 [38.8%] women and 2622 [61.2%] men), 2076 had a spinal drain placed. Propensity matching yielded 1292 pairs with adequate covariate balance (all 44 absolute standardized differences <0.1). In the 2584 propensity-matched patients, spinal drain placement was associated with a reduced risk of SCI (1.5% vs 2.5%; risk-adjusted odds ratio [OR], 0.47; 95% confidence interval [CI], 0.24-0.89; P = .02). The rates of 30-day mortality (4.5% vs 5.0%; risk-adjusted OR, 0.67; 95% CI, 0.44-1.01; P = .05) and prolonged intensive care unit stay (7.0% vs 5.7%; risk-adjusted OR, 1.10; 95% CI, 0.84-1.45; P = .48) did not differ on the basis of spinal drain placement. The crossover rate was 10% (127/1292), and those with postoperative drain placement had a 20% (26/127) SCI rate on discharge. CONCLUSIONS: Among patients undergoing thoracic and thoracoabdominal endovascular aortic repair, preoperative placement of a spinal drain, compared with no drain, was associated with reduced risk of SCI. Cerebrospinal fluid drainage as a rescue measure does not provide the same protection offered by routine preoperative placement. Further investigation, including randomized controlled trials, is needed to more definitively determine the role for spinal drainage in TEVAR.

Highly pathogenic avian influenza A(H7N3) virus in poultry workers, Mexico, 2012.

We identified 2 poultry workers with conjunctivitis caused by highly pathogenic avian influenza A(H7N3) viruses in Jalisco, Mexico. Genomic and antigenic analyses of 1 isolate indicated relatedness to poultry and wild bird subtype H7N3 viruses from North America. This isolate had a multibasic cleavage site that might have been derived from recombination with host rRNA.

A (H1N1) pdm09 HA D222 variants associated with severity and mortality in patients during a second wave in Mexico.

BACKGROUND: Pandemic type A (H1N1) influenza arose in early 2009, probably in Mexico and the United States, and reappeared in North America in September for seven more months. An amino acid substitution in the hemagglutinin (HA), D222G, has been reported in a significant proportion of patients with a severe and fatal outcome. We studied the prevalence of HA222 substitutions in patients in Mexico during the second wave and its association with clinical outcome and pathogenicity in a mouse model. METHODS: The nucleotide sequences of hemagglutinin (HA) from viruses collected from 77 patients were determined including 50 severe and fatal cases and 27 ambulatory cases. Deep sequencing was done on 5 samples from severe or fatal cases in order to determine the quasispecies proportion. Weight loss and mortality due to infection with cultured influenza viruses were analyzed in a mouse model. RESULTS: Viruses from 14 out of 50 hospitalized patients (28%) had a non aspartic acid residue at the HA 222 position (nD222), while all 27 ambulatory patients had D222 (p=0.0014). G222 was detected as sole species or in coexistence with N222 and D222 in 12 patients with severe disease including 8 who died. N222 in coexistence with D222 was detected in 1 patient who died and co-occurrence of A222 and V222, together with D222, was detected in another patient who died. The patients with a nD222 residue had higher mortality (71.4%), compared to the group with only D222 (22.2%, p=0.0008). Four of the 14 viruses from hospitalized patients were cultured and intranasally infected into mice. Two viruses with G222 were lethal while a third virus, with G222, caused only mild illness in mice similar to the fourth virus that contained D222. CONCLUSIONS: We confirm the elevated incidence of HA222 (H1N1)pdm09 variants in severe disease and mortality. Both clinical and mouse infection data support the idea that nD222 mutations contribute to increased severity of disease but additional determinants in disease outcome may be present.

Mortality Analysis of Patients with COVID-19 in Mexico Based on Risk Factors Applying Machine Learning Techniques.

The new pandemic caused by the COVID-19 virus has generated an overload in the quality of medical care in clinical centers around the world. Causes that originate this fact include lack of medical personnel, infrastructure, medicines, among others. The rapid and exponential increase in the number of patients infected by COVID-19 has required an efficient and speedy prediction of possible infections and their consequences with the purpose of reducing the health care quality overload. Therefore, intelligent models are developed and employed to support medical personnel, allowing them to give a more effective diagnosis about the health status of patients infected by COVID-19. This paper aims to propose an alternative algorithmic analysis for predicting the health status of patients infected with COVID-19 in Mexico. Different prediction models such as KNN, logistic regression, random forests, ANN and majority vote were evaluated and compared. The models use risk factors as variables to predict the mortality of patients from COVID-19. The most successful scheme is the proposed ANN-based model, which obtained an accuracy of 90% and an F1 score of 89.64%. Data analysis reveals that pneumonia, advanced age and intubation requirement are the risk factors with the greatest influence on death caused by virus in Mexico.

Is ultra-violet radiation the main force shaping molecular evolution of varicella-zoster virus?

BACKGROUND: Varicella (chickenpox) exhibits a characteristic epidemiological pattern which is associated with climate. In general, primary infections in tropical regions are comparatively less frequent among children than in temperate regions. This peculiarity regarding varicella-zoster virus (VZV) infection among certain age groups in tropical regions results in increased susceptibility during adulthood in these regions. Moreover, this disease shows a cyclic behavior in which the number of cases increases significantly during winter and spring. This observation further supports the participation of environmental factors in global epidemiology of chickenpox. However, the underlying mechanisms responsible for this distinctive disease behavior are not understood completely. In a recent publication, Philip S. Rice has put forward an interesting hypothesis suggesting that ultra-violet (UV) radiation is the major environmental factor driving the molecular evolution of VZV. DISCUSSION: While we welcomed the attempt to explain the mechanisms controlling VZV transmission and distribution, we argue that Rice's hypothesis takes lightly the circulation of the so called "temperate VZV genotypes" in tropical regions and, to certain degree, overlooks the predominance of such lineages in certain non-temperate areas. Here, we further discuss and present new information about the overwhelming dominance of temperate VZV genotypes in Mexico regardless of geographical location and climate. SUMMARY: UV radiation does not satisfactorily explain the distribution of VZV genotypes in different tropical and temperate regions of Mexico. Additionally, the cyclic behavior of varicella does not shown significant differences between regions with different climates in the country. More studies should be conducted to identify the factors directly involved in viral spreading. A better understanding of the modes of transmissions exploited by VZV and their effect on viral fitness is likely to facilitate the implementation of preventive measures for disease control.

Soil Microbial Communities Associated With Biodegradable Plastic Mulch Films.

Agricultural plastic mulch films provide a favorable soil microclimate for plant growth, improving crop yields. Biodegradable plastic mulch films (BDMs) have emerged as a sustainable alternative to widely used non-biodegradable polyethylene (PE) films. BDMs are tilled into the soil after use and are expected to biodegrade under field conditions. However, little is known about the microbes involved in biodegradation and the relationships between microbes and plastics in soils. In order to capture the consortium of soil microbes associated with (and thus likely degrading) BDMs, agriculturally-weathered plastics from two locations were studied alongside laboratory enrichment experiments to assess differences in the microbial communities associated with BDMs and PE films. Using a combination of amplicon sequencing and quantitative PCR (qPCR), we observed that agriculturally-weathered plastics hosted an enrichment of fungi and an altered bacterial community composition compared to the surrounding soil. Notably, Methylobacterium, Arthrobacter, and Sphingomonas were enriched on BDMs compared to non-biodegradable PE. In laboratory enrichment cultures, microbial consortia were able to degrade the plastics, and the composition of the microbial communities was influenced by the composition of the BDMs. Our initial characterization of the microbial communities associated with biodegradable plastic mulch films, or the biodegradable "plastisphere," lays the groundwork for understanding biodegradation dynamics of biodegradable plastics in the environment.

Foraging Bumblebees Selectively Attend to Other Types of Bees Based on Their Reward-Predictive Value.

Using social information can be an efficient strategy for learning in a new environment while reducing the risks associated with trial-and-error learning. Whereas social information from conspecifics has long been assumed to be preferentially attended by animals, heterospecifics can also provide relevant information. Because different species may vary in their informative value, using heterospecific social information indiscriminately can be ineffective and even detrimental. Here, we evaluated how selective use of social information might arise at a proximate level in bumblebees (Bombus terrestris) as a result of experience with demonstrators differing in their visual appearance and in their informative value as reward predictors. Bumblebees were first trained to discriminate rewarding from unrewarding flowers based on which type of "heterospecific" (one of two differently painted model bees) was next to each flower. Subsequently, these bumblebees were exposed to a novel foraging context with two live painted bees. In this novel context, observer bumblebees showed significantly more social information-seeking behavior towards the type of bees that had predicted reward during training. Bumblebees were not attracted by paint-marked small wooden balls (moved via magnets) or paint-marked non-pollinating heterospecifics (woodlice; Porcellio laevis) in the novel context, indicating that bees did not simply respond to conditioned color cues nor to irrelevant social cues, but rather had a "search image" of what previously constituted a valuable, versus invaluable, information provider. The behavior of our bumblebees suggests that their use of social information is governed by learning, is selective, and extends beyond conspecifics.

EV-D68 infection in children with asthma exacerbation and pneumonia in Mexico City during 2014 autumn.

BACKGROUND: Human enterovirus D68 (EV-D68) recently caused an increase in mild-to-severe pediatric respiratory cases in North America and some European countries. Even though few of these children presented with acute paralytic disease, direct causal relationship cannot yet be assumed. OBJECTIVES: The purposes of this report were to describe the clinical findings of an outbreak of EV-D68 infection in Mexico City and identify the genetic relationship with previously reported strains. PATIENTS/METHODS: Between September and December 2014, 126 nasopharyngeal samples (NPS) of hospitalized children <15 years of age with ARI were tested for the presence of respiratory viruses using a multiplex RT-qPCR and EV-D68-specific RT-qPCR. Clinical, epidemiological, and demographic data were collected and associated with symptomatology and viral infections. Phylogenetic analyses were performed using VP1 region. RESULTS: Enterovirus/rhinovirus infection was detected in 40 patients (31·7%), of which 24 patients were EV-D68-positive. EV-D68 infection prevailed over September and October 2014 and was associated with neutrophilia and lymphopenia, and patients were more likely to develop hypoxemia. Phylogenetic analyses showed that Mexican EV-D68 belongs to the new B1 clade. CONCLUSIONS: This is the first EV-D68 outbreak described in Mexico and occurred few weeks after the United States reported similar infections. Although EV-D68 belongs to new B1 clade, no neurological affection was observed.

An outbreak of leptospirosis among Peruvian military recruits.

Acute undifferentiated febrile illnesses are common in tropical developing countries but are difficult to diagnose on clinical grounds alone. Leptospirosis is rarely diagnosed, despite evidence that sporadic cases and epidemics continue to occur worldwide. The purpose of this study was to diagnose an outbreak of acute undifferentiated febrile illness among Peruvian military recruits that developed after a training exercise in the high jungle rainforest of Peru. Of 193 military recruits, 78 developed an acute febrile illness with varied manifestations. Of these, 72 were found to have acute leptospirosis by a microscopic agglutination test (MAT). An enzyme-linked immunosorbent assay using Leptospira biflexa antigen was insensitive for the detection of anti-leptospiral IgM antibodies compared with the MAT (20 of 72, 28%). This outbreak of acute undifferentiated febrile illness among Peruvian military recruits was due to leptospirosis. High clinical suspicion, initiation of preventative measures, and performance of appropriate diagnostic testing is warranted in similar settings to identify, treat, and prevent leptospirosis.

Mitología y Medicina I: Dioses griegos primigenios de la Medicina Occidental / Mythology and medicine I: Original greek gods of Western Medicine

La práctica médica en la antigua Grecia se llevó a cabo en dos vertientes: una medicina de carácter místico religioso, enraizada en las creencias politeístas, donde dioses sanadores acudían a los santuarios (asclespiades) para ayudar a los enfermos; y una concepción médica, de carácter naturalistico, empírico y racional, ejecutada por médicos entrenados en las escuelas de medicina. Estas dos prácticas no están reñidas entre sí, la primera da paso a la segunda forma de enfrentar el proceso salud-enfermedad, ya que está basada más en prácticas de suturas de heridas superficiales, espolvoreo de sustancias naturales cicatrizantes y/o analgésicas, y aplicación de brebajes de hierbas medicinales, pero es una medicina, cuya narración mitológica ya se encuentra lejos de las prácticas mágica religiosa o milagros de curación espontánea; mientras que la actitud de los médicos científicos es de respeto de las prácticas religiosas de restitución de la salud, aunque ellos ofrezcan servicios limitados al pronóstico del paciente y de carácter laico y sin rituales religiosos. El presente artículo pretende explorar las deidades primigenias de la salud (Quirón, Apolo y Asclepios) y cómo los rituales, símbolos y significados religiosos asignados en sus ceremonias religiosas, representaciones artísticas, y concepciones teológicas, siguen influyendo en la concepción y expresión sociocultural y ética de la práctica médica científica del mundo occidental actual. La concepción mitológica de la medicina impregna las prácticas modernas de la misma, en su expresión sociocultural, simbólica y ética, pero conservando el respeto a la acción autónoma, laica, apolítica y racional.

Medical practice in the ancient Greece was carried out in two ways: a mystical religious medicine, rooted in the polytheistic beliefs, where healing gods flocked to shrines (asclepiads) to help the sick; and a medical concept of naturalistic, empirical and rational character, performed by physicians trained in medical schools. These two practices are not at odds with themselves, the first opens the door to the second way of confronting the health-disease process, since it is based more on practices of sutures of superficial wounds, sprinkling of natural substances healing the analgesic, and application of herbal concoctions, but is a medicine, whose mythological narrative is already away from religious magic practices or miracles of spontaneous healing; while the attitude of the scientific physicians is one of respect for the religious restoration of health practices, even though they offer limited services to the prognosis of the patient and secular nature and without religious rituals. This article aims to explore the primordial deities of health (Chiron, Apollo and Asclepius) and how the rituals, the symbols and religious meanings assigned to their religious ceremonies, artistic depictions, and theological concepts, are still influencing the conception, socio-cultural expression and ethical practice of the medical science in the Western world today. The mythological conception of medicine permeates modern practices, in its socio-cultural, symbolic and ethical expressions, while retaining respect for the autonomous, secular, apolitical and rational action.

El láser ¿motivación o realidad para el estudio de física por los estudiantes de las Ciencias para la Salud? / Laser, motivation or reality for the study of physics by health sciences students?

Se realizó este estudio para que sirviera de instrumento de trabajo y de fuente de consulta a los estudiosos e interesados en el tema. La palabra láser es una sigla de las palabras inglesas light amplification by stimulated emission of radiation ¿qué cantidad de estudiantes conocen el significado de estas palabras, aun conociendo su traducción al español? Para lograr este producto informativo que lleva hacia el estudio y la comprensión de la Física, fue necesario realizar una labor de búsqueda y síntesis de la información publicada sobre el asunto en libros, revistas y obras de referencia. En cuanto a su estructura, se presentó en forma cronológica y descriptiva la iniciación, desarrollo, generalidades del láser y su utilización en las Ciencias para la Salud

Análisis de la disciplina Histología en el plan de estudio de la carrera de Medicina / Analysis of Histology as a discipline in the curriculum of the medical career

Se explica la estructura de una disciplina y de una asignatura dentro del curriculum, con especial énfasis en la disciplina Histología en el plan de estudio de la carrera de medicina. Se proponen posibles adecuaciones. Se analiza la asignatura Histología I, y se encuentran dificultades en el sistema de evaluación y en la selección de los tipos de clase donde se analizan las evaluaciones frecuentes: por lo que se pierde la coordinación entre los objetivos, los contenidos y el sistema de evaluación

The structure of a discipline and of a subject within the curriculum is explained, making special emphasis on the discipline of Histology in the medical curriculum. Possible adaptations are recommended. Histology I is analyzed as a subject and difficulties are found in the system of evaluation and in the selection of the types of class where the frequent evaluations are analyzed. That's why, the coordination among the objectives, the content and the system of evaluation is lost

La edad materna y su influencia en algunos trastornos perinatales / Maternal age and its influence on some perinatal disorders

Se revisaron los registros de nacimiento ocurridos en los años de 1985 y 1986 en el Hospital Ginecoobstétrico "Héroes de Playa Giróm" de Coenfuegos, además de 257 placentas de igual número de partos ocurridos en el período de enero a diciembre de 1986 en dicho centro. Se determinó la relación entre la edad materna, el peso del recién nacido y la morfología placentaria; se señala la incidencia de embarazos en la adolescencia en nuestras provincias con vistas a evaluar el nivel de educación sexual de la población y las consecuencias que puede traer para el futuro hijo

El embarazo en la adolescencia: un problema de salud actual / Pregnancy in adolescents: a presently health problem

Se analizaron los nacimientos ocurridos en el Hospital Ginecobstétrico Provincial de Cienfuegos durante los años 1985, 1986 y 1987, para determinar los nacimientos de niños de madres menores menores de 20 años. Se observó una disminución progresiva de partos en la adolescencia en el período estudiado, auque la cifra todavía es elevada. También pudo comprobarse una disminución significativa del peso del recién nacido del grupo estudio comparado con el del grupo control: así como fueron inferiores los resultados de la morfología placentaria, lo que manifiesta su relación no sólo con la edad de la madre sino con el peso del recién nacido

La edad materna y su influencia en algunos parámetros perinatales / The maternal age and its influence in some perinatal parameters

Se estudió la influencia de la edad materna en la aparición de los trastornos perinatales en nuestra provincia, dada la importancia que para nuestros profesionales de la salud posee este tema. Se revisaron los nacimientos ocurridos en los años 1985 y 1986 en el Hospital Gineco-Obstétrico "Héroes de Playa Girón" de Cienfuegos, para lo que se dividieron en tres grupos las edades de las madres: -de 20 años, de 20 a 34 y más de 34 años. se analizaron además, 257 placentas de igual número de partos a término, ocurridos en el período de enero a diciembre de 1986 en dicho centro con lo que quedó demostrado en la muestra estudiada, que el embarazo en la adolescencia, tuvo una elevada frecuencia en los años 1985 y 1986. es evidente la relación entre la edad materna y el peso de la placenta, donde la diferencias entre los tres grupos estudiados, fueron significativas, así como la relación con el peso del recién nacido, en que diferencias entre los grupos de edades incluidos en el trabajo, fueron altamente significativas

Quiste neuroepitelial intracerebral: reporte de un caso revisión de su histogénesis / Intracerebral neuroepithelial cyst: report of a case and review of its histogenesis

Presentamos un caso de Quiste Neuroepitelial Intracerebral yuxta ventricular en una mujer joven, en donde se había practicado resección hace quince años y que permaneció asintomático hasta comportarse como una lesión ocupante de espacio con hipertensión endocraneana; discutimos los quistes neuroepiteliales del neuroeje en relación a su histogénesis y comportamiento clínico-patológico y revisamos la literatura correspondiente a estos raros casos