Induced Changes In Structure Research Articles

Poling induced changes in polarization domain structure of polymer ferroelectrics for application in organic thin film transistors

While electrical poling of organic ferroelectrics has been shown to improve device properties, there are challenges in visualizing accompanying structural changes. We observe poling induced changes in ferroelectric domains by applying differential phase contrast (DPC) imaging in the scanning transmission electron microscope, a method that has been used to observe spatial distributions of electromagnetic fields at the atomic scale. In this work, we obtain DPC images from unpoled and electrically poled polyvinylidene fluoride trifluorethylene films and compare their performance in polymer thin film transistors. The vertically poled films show uniform domains throughout the bulk compared to the unpoled film with a significantly higher magnitude of the overall polarization. Thin film transistors comprising a donor–acceptor copolymer as the active semiconductor layer show improved performance with the vertically poled ferroelectric dielectric film compared with the unpoled ferroelectric dielectric film. A poling field of 80–100 MV/m for the dielectric layer yields the best performing transistors; higher than 100 MV/m is seen to degrade the transistor performance. The results are consistent with a reduction in deleterious charge carrier scattering from ferroelectric domain boundaries or interfacial dipoles arising from electrical poling.

Non-innocent P-centers in nonbenzenoid polycyclic aromatic molecules with tunable structures and properties.

Implanting heteroatoms into polycyclic aromatic molecules (PAMs) offers a great opportunity to fine-tune their optoelectronic properties. Herein, we report a new type of nonbenzenoid PAM in which the sp2 C atoms are replaced by S and P in the azulene moiety. The synthesis harnessed modular P-chemistry and cyclization chemistry, which afforded the first example of P-azulene-based PAMs with isomeric PN- and PC-type structures. Photophysical and theoretical studies revealed that the P-environments have strong impacts on the structures and properties of the P-PAMs. Different from the electronic structure of azulene with strong π conjugation, the PC derivatives maintained effective σ*-π* hyperconjugation in the frontier molecular orbitals via the P-centers. In particular, the PC derivative with a P(iii)-center showed unexpected room-temperature phosphorescence in solution, which was attributed to the excited-state aromaticity induced structure change at the P-center. Decoration with various aryl groups further modified the photophysical and redox properties in another dimension. Furthermore, bis(triarylamine)-functionalized P-PAMs formed stable radical cations in which the P-environments strongly influenced the mixed-valence state and open-shell characters. As a proof of concept, bis(triarylamine)-functionalized P-PAMs were explored as the hole-transporting layers in perovskite solar cells, and a power conversion efficiency of 14% was achieved. As a new example of nonbenzenoid PAMs with intriguing optoelectronic properties, our P-PAMs are promising building blocks for diverse optoelectronic applications in the future.

Modeling the partitioning of amphiphilic molecules and co-solvents in biomembranes

Amphiphilic co-solvents can have a significant impact on the structure, organization and physical properties of lipid bilayers. Describing the mutual impact of partitioning and induced structure changes is therefore a crucial consideration for a range of topics such as anesthesia and other pharmacokinetic effects, as well as microbial solvent tolerance in the production of biofuels and other fermentation products, where molecules such as ethanol, butanol or acetic acid might be generated. Small-angle neutron scattering (SANS) is a key method for studying lipid and polymer bilayer structures, with many models for extracting bilayer structure (thickness, area per lipid etc.) from scattering data in use today. However, the molecular details of co-solvent partitioning are conflated with induced changes to bilayer structure, making interpretation and modeling of the scattering curves a challenge with the existing set of models. To address this, a model of a bilayer structure is presented which invokes a two-term partition constant accounting for the localization of the co-solvent within the bilayer. This model was validated using a series of SANS measurements of lipid vesicles in the presence of the co-solvent tetrahydrofuran (THF), showing several strategies of how to deploy the two-parameter partition constant model to describe scattering data and extract both structure and partitioning information from the data. Molecular dynamics simulations are then used to evaluate assumptions of the model, provide additional molecular scale details and illustrate its complementary nature to the data fitting procedure. This approach results in estimates of the partition coefficient for THF in 1,2-dimyristoyl-sn-glycero-3-phosphocholine at 35°C, along with an estimate of the fraction of THF residing in the hydrophobic core of the membrane. The authors envision that this model will be applicable to a wide range of other bilayer/amphiphile interactions and provide the associated code needed to implement this model as a fitting algorithm for scattering data in the SasView suite.

Rf Magnetron Sputtering Power Induced Changes in Structure and Properties of (Tivcrnbsitaby)N High-Entropy Alloy Nitride Coatings

Rf Magnetron Sputtering Power Induced Changes in Structure and Properties of (Tivcrnbsitaby)N High-Entropy Alloy Nitride Coatings

Surface oxygen vacancies formation on Zn2SnO4 for bisphenol-A degradation under visible light: The tuning effect by peroxymonosulfate

Visible light catalysis has been widely coupled with persulfate activation for refractory pollutants removal, while the exact role of persulfate played in such composite system is still questionable. In this work, the relation between peroxymonosulfate (PMS) induced structure change and visible light responsive activity of inverse spinel: i.e., Zn2SnO4, was deciphered. Under the visible light illumination (λ>420nm) PMS addition would endow the composite system with pollutant removal performance. Batch test revealed that 60% of bisphenol-A (5 mg L−1) was mineralized within 3 h reaction time, by dosing 0.81 mM PMS and 0.1 g L−1 catalyst. The above oxidative system was also effective for other refractory pollutants elimination. Further analysis indicated that PMS could reduce the band gap of spinel from 2.75 to 2.52 eV and thereby enabling its visible light activity. Photogenerated h+ induced •OH and e- mediated •O2− contributed to the pollutant removal while h+ played a leading role. Density functional theory revealed that PMS would capture oxygen atom of spinel and induce surface oxygen vacancy defect structure formation. Also, three-oxygen atom coordinated Zn was identified as the possible catalyze site. This work is valuable for deep understanding the exact role of persulfate in photocatalytic system.

Discovering Hybrid Plasmonic Nanocatalysts for Solar-Chemical Energy Conversion via Femtosecond Pulsed Laser-Induced Atomic Redistribution in Bimetallic Au-Pd Nanorods

Utilizing solar energy for chemical transformations has attracted a growing interest in promoting the clean and modular chemical synthesis approach and addressing conventional thermocatalytic systems’ limitations. Photoelectrochemical (PEC) cells enabling the conversion of solar energy to storable and transportable fuels could address the existing challenge of mismatch between renewable energy supply and demand. Understanding the electronic and thermal properties of metal nanoparticles and their interactions with other materials is imperative to improve PEC cells’ efficiency. PECs typically consist of architecturally sophisticated photoelectrocatalysts assembled into a structure designed to optimize light harvesting and catalytic chemical transformations. Physical and chemical processes critical to PEC cells’ operation occur at the electrode-electrolyte interface. After plasmonic excitation of metal with incident light, the plasmon can quickly dephase through electronsurface scattering on a few femtosecond (fs) time scales, generating nonthermal electrons. Before non-thermal hot electrons lose energy to the surrounding medium, they can excite electronic or vibrational transitions in adsorbed molecules on the nanoparticle’s surface, thus enabling photocatalytic reactions.Under light irradiation, noble metal nanoparticles, particularly those characterized by localized surface plasmon resonance, commonly known as plasmonic nanoparticles, generate a strong electromagnetic field, excited hot carriers, and photothermal heating. Plasmonic nanoparticles enabling efficient absorption of light in the visible range have moderate catalytic activities. However, the catalytic performance of a plasmonic nanoparticle can be significantly enhanced by incorporating a highly catalytically active metal domain onto its surface. In this study, we demonstrate that femtosecond laser-induced atomic redistribution of metal domains in bimetallic Au-Pd nanorods (NRs) can enhance its photocurrent response by two-fold compared to parent Au-Pd NRs. We induce structure changes on Au-Pd NRs by irradiating them with femtosecond pulsed laser at 808 nm to precisely redistribute Pd atoms on AuNRs surfaces, resulting in modified electronic and optical properties thereby an enhanced catalytic activity. We also investigate the trade-off between the effect of light absorption and catalytic activity by optimizing the structure and composition of bimetallic Au-Pd nanoparticles. This work provides insight into the design of hybrid plasmonic-catalytic nanostructures with well-tailored geometry, composition, and structure for solar-fuel-based applications.This material is based upon work supported by the National Science Foundation under Grant No. 1904351. Figure 1

Role of Femtosecond Pulsed Laser-Induced Atomic Redistribution in Bimetallic Au-Pd Nanorods on Optoelectronic and Catalytic Properties.

Utilizing solar energy for chemical transformations has attracted a growing interest in promoting the clean and modular chemical synthesis approach and addressing the limitations of conventional thermocatalytic systems. Under light irradiation, noble metal nanoparticles, particularly those characterized by localized surface plasmon resonance, commonly known as plasmonic nanoparticles, generate a strong electromagnetic field, excited hot carriers, and photothermal heating. Plasmonic nanoparticles enabling efficient absorption of light in the visible range have moderate catalytic activities. However, the catalytic performance of a plasmonic nanoparticle can be significantly enhanced by incorporating a highly catalytically active metal domain onto its surface. In this study, we demonstrate that femtosecond laser-induced atomic redistribution of metal domains in bimetallic Au-Pd nanorods (NRs) can enhance its photocurrent response by 2-fold compared to parent Au-Pd NRs. We induce structure changes on Au-Pd NRs by irradiating them with a femtosecond pulsed laser at 808 nm to precisely redistribute Pd atoms on AuNR surfaces, resulting in modified electronic and optical properties and, thereby, enhanced catalytic activity. We also investigate the trade-off between the effect of light absorption and catalytic activity by optimizing the structure and composition of bimetallic Au-Pd nanoparticles. This work provides insight into the design of hybrid plasmonic-catalytic nanostructures with well-tailored geometry, composition, and structure for solar-fuel-based applications.

Pore/fracture structure and gas permeability alterations induced by ultrasound treatment in coal and its application to enhanced coalbed methane recovery

Ultrasonic treatment is a highly potential method for reservoir permeability modification in enhanced coalbed methane recovery. Quantitative evaluations of ultrasonic induced changes in structure and permeability in coal are of great interest for potential field applications of ultrasound technology. In this study the scanning electron microscope (SEM) and low-temperature liquid nitrogen (LTLN) were used to examine the ultrasound induced alterations in coal pore/fracture, and further measured gas permeability in coal by coupling the ultrasound field and external stress. The SEM images show that ultrasound treatment can extend the original pore/fracture, increase the connectivity and remove barriers in gas seepage channel in coal. The LTLN data reveals that with the ultrasonic treatment (25 kHz, 18 kW, 2 h), the maximum N 2 adsorption quantity of the tested samples increased by 106.5%–258.4%, and the average pore diameter increased by 37.06%–81.40%; the specific surface area increased by 94.80%–118.15%, and the total pore volume increased by 87.12%–252.55%. It implies that coal pores in size ranging from 1 nm to 100 nm can be remarkably improved by ultrasonic treatment, which is significant beneficial to promote gas desorption/diffusion within coal matrix. Permeability tests demonstrate that gas permeability in stressed coal increased by 29.3%–57.1% with the implement of ultrasound field (25 kHz, 18 kW, 30 min). Ultrasonic performance on permeability improvement is proportional to the treatment time, but the function of ultrasonic fracturing has time threshold effect, and after a certain period of treatment, the ultrasonic fracturing performance becomes very limited in stressed coal. • Coal pore/fracture structure alterations induced by ultrasound treatment is examined using SEM and LTLN techniques . • Ultrasound treatment significantly increases the N 2 accessible specific surface area and pore volume in coal. • External stress and ultrasound treatment time influences gas permeability behavior in coal induced by ultrasonic fracturing. • A conceptual field application scheme of ultrasonic fracturing for enhanced CBM recovery is proposed.

Correlated Post-mortem Raman and TEM Investigation of Nanoindentation Induced Structural Changes in Silicon as a Function of Temperature

Correlated Post-mortem Raman and TEM Investigation of Nanoindentation Induced Structural Changes in Silicon as a Function of Temperature

Influence of thermally induced structure changes in diluted β-lactoglobulin solutions on their surface activity and behavior in foam fractionation

Surface activity is an intrinsic protein feature, leading to the capability of aqueous protein solutions to form foam. This feature provides opportunities for downstream processing, such as usage of foam fractionation for purification. In order to investigate the impact of the surface activity on the performance of the foam fractionation process, protein solutions with different surface activity were produced by different thermal denaturation of aqueous β-lactoglobulin solutions. The effectiveness of the denaturation procedure was verified with circular dichroic spectroscopy, and the impact on surface activity was determined via dynamic surface tension measurement. The increased surface activity resulted in higher foamate flow rates. Furthermore, the effects could be correlated with secondary structure changes and with the dynamic surface pressure. The new result of this study is that the effect of the denaturation of a protein on foam fractionation depends on the protein concentration. At the lower feed concentration, effects became visible, which could not be observed at the higher concentration.

Фазовые превращения в оксидах железа под действием микроволнового излучения

It is shown that microwave radiation induces structure changes and, consequently, magnetic phase transitions in iron oxide alpha-Fe2O3. We subjected finely dispersed partially amorphized particles of iron oxide Fe2O3 to 10-minute-long microwave field treatment in a humid air environment. This resulted in a reduction of the hematite crystalline phase by 40%. At the same time the total fraction of crystalline components increased due to the creation of a new ferromagnetic modification which is maghemite alpha-Fe2O3. The original antiferromagnetic samples and the finial ferrimagnetic batches were powders composed of spherical particles with similar values of the area of a coherent X-ray scattering area (40-60 nm).

Microwave-induced phase transformations of iron oxide particles

The article presents results of study of α-Fe2O3 response on microwave treatment. Microwave influence on iron oxides constituting nature occurring kaolinite clay were studied by a complex of methods. The original sample S0 was made from fine-dispersed Fe2O3 iron oxide particles. Sample S1 was produced via treatment with 2.45 GHz microwave field. Microwave treatment induced structure changes in iron oxides which manifest themselves through polymorphic changes. X-ray phase analysis shown that a deformation polymorphic transformation α-Fe2O3→γ-Fe2O3 takes place and two-phase hematite-maghemite state is formed. Problem of faint and overlapping diffraction peaks resolution is solved with wavelet transformation skeleton technique. Crystal particles of S0 sample are α-Fe2O3 hematite particles with rhombohedral lattice. After microwave treatment sample S1 developed new diffraction peaks corresponding to cubic γ-Fe2O3 maghemite crystal system. Polymorphic transition is accompanied with morphological changes. After the treatment surfaces of large particles are covered with smaller particles which are proved by the increase of samples fractal dimension from 2.83 to 2.85. Powder color changes from red-orange to dark brown which results in changes of all color parameters; the red component experience the biggest suppression and it is suppressed by the factor 2.

Reactive Milling Induced Structure Changes in Phenylphosphonic Acid Functionalized LiMn2O4 Nanocrystals – Synthesis, Rietveld Refinement, and Thermal Stability

Spinel LiMn2O4 formed in a solid‐state reaction was treated with a high energy planetary ball mill. A mechanochemical in situ surface functionalization of the nanocrystallites with a size smaller than 10 nm was achieved by addition of phenylphosphonic acid. The functionalization was proven by infrared spectroscopy and it can be shown that it prevents the formation of Mn2O3 during the milling process. Structural changes of the samples were investigated via XRD and Rietveld refinement. Mild milling conditions induce an anisotropic broadening of the reflections caused by a distribution of lattice parameters. In this first stage, we propose a structure model based on orthorhombic LiMn2O4. DSC and in situ XRD measurements also verify the presence of the orthorhombic low temperature phase. Medium milling conditions induce a change of intensities, correlated to a cation disorder. Harsher milling conditions induce the transformation to a tetragonal phase. The thermal stability of the formed phases was investigated via in situ high temperature XRD. The reformation of cubic spinel is observed in all samples; however, the transition point depends on the previous milling parameters.

ИНФРАКРАСНАЯ СПЕКТРОСКОПИЯ КАК МЕТОД ОПРЕДЕЛЕНИЯ СТРУКТУРНЫХ ОТКЛИКОВ ПРИРОДНЫХ ГЛИН НА СВЧ-ВОЗДЕЙСТВИЕ

Методом ИК-спектроскопии изучены структурные отклики частиц монтмориллонитовой и каолинитовой глин месторождений Оренбургской области на СВЧ-воздействие. Обработку проб в течение 10 минут проводили в поле магнетрона мощностью 750 Вт в воздушной и влажной средах. Спектры получены с помощью ИК-Фурье спектрометра в диапазоне длин волн 4000–400 cм-1. Установлено, что в монтмориллонитовой глине количество доминирующих связей в тетраэдре SiO4 снижается в 1.5 раза при обработке в сухом воздухе и в 1.8 раза – во влажном. В глине, содержащей каолинит, все типы связей активно разрушаются под воздействием СВЧ-поля.
 
 
 ИСТОЧНИК ФИНАНСИРОВАНИЯРабота выполнена при финансовой поддержке РФФИ и правительства Оренбургской области в рамках научного проекта № 19-43-560001 р_а «Физико-химические принципы процессов СВЧ-консолидации каолинитов».
 
 
 
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Annealing Behavior with Thickness Hindered Nucleation in Small-Molecule Organic Semiconductor Thin Films

We introduce a comprehensive overview of spontaneous and thermal induced structure changes in thin films of the high performance small-molecular organic semiconductor 5,11-bis(triethyl silylethynyl) anthradithiophene (TES-ADT). Most importantly, we find that nucleation of the TES-ADT high temperature beta phase can be induced only for films thicker than a critical thickness, while it is hindered for thinner films. The described limited crystal phase nucleation, the circumstances of which are unique in the realm of small-molecule organic semiconductors, is explained in terms of a two step nucleation mechanism while taking into account the anisotropic surface energy of crystal grains. Furthermore, we identify changes in the optical absorption spectra observed during aging of as deposited films with a spontaneous transformation from the amorphous phase to the alpha(2) phase via the alpha(1) phase of TES-ADT. The transformation takes place on the time scale of several days. Finally, we determine temperature dependence of lattice parameters of the alpha(1) and alpha(2) phases and the lattice parameters of the beta phase. Thermal expansion of the alpha(1) phase is found to be much lower than that of the alpha(2) phase.

Effect of gamma-irradiation on the structural, optical and electrical properties of PEO/starch blend containing different concentrations of gold nanoparticles

ABSTRACTBlend of polyethylene oxide (PEO)/starch (70/30 wt.%) filled with different amounts of gold nanoparticles (AuNPs) were prepared using the casting technique. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) techniques were used to investigate the structure of polymeric samples before and after exposing to gamma irradiation at different times. XRD showed a gradual decrease in intensity of crystalline peaks with increasing the gamma dose denotes a decrease in the amount of crystalline phase in the films, while the FTIR measurement shows induced changes in chemical structure assigned to the AuNPs amount and irradiation times. The optical energy gap values (Eg) for unirradiated and irradiated samples were calculated and interpreted. The differential scanning calorimetry (DSC) which showed the miscibility between the two components of the blend. The electrical conductivity (σ) measurement was showed increased in electrical conductivity after exposure to the gamma dose. The gold nanoparticles were used as nanofiller to improve the structural and electrical properties of polymeric samples. The results showed the Gamma irradiation significantly effect on the structural and electrical properties of PEO/starch blend.

Ratiometric Photoacoustic Nanoprobe for Bioimaging of Cu2.

Aberrant copper contents implicate numerous diseases including Alzheimer's disease and Wilson's disease. Conventional copper detection technologies are difficult to offer non-invasive and accurate deep tissue detection of copper. Here, we report a photoacoustic (PA) nanoprobe (NRh-IR-NMs) for ratiometric PA imaging of Cu2+. The nanoprobe consists of a selective Cu2+-responsive probe (NRh) as the indicator and a nonresponsive dye (IR) as the internal reference. In the presence of Cu2+, a selective Cu2+-induced structure change of NRh would take place, resulting in the increase of PA signal intensity increment at 716 nm (ΔPA716). However, the ΔPA834 which attributes to IR shows negligible change. Therefore, the ratiometric PA signal (ΔPA716/ΔPA834) could be used as an indicator for Cu2+ detection. This ratiometric PA detection method offers a noninvasive technology with high selectivity and tissue penetration depth, which is a promising tool for deep-tissue detection of Cu2+ in living organisms.

Using vibrational molecular spectroscopy to reveal association of steam-flaking induced carbohydrates molecular structural changes with grain fractionation, biodigestion and biodegradation

Advanced vibrational molecular spectroscopy has been developed as a rapid and non-destructive tool to reveal intrinsic molecular structure conformation of biological tissues. However, this technique has not been used to systematically study flaking induced structure changes at a molecular level. The objective of this study was to use vibrational molecular spectroscopy to reveal association between steam flaking induced CHO molecular structural changes in relation to grain CHO fractionation, predicted CHO biodegradation and biodigestion in ruminant system. The Attenuate Total Reflectance Fourier-transform Vibrational Molecular Spectroscopy (ATR-Ft/VMS) at SRP Key Lab of Molecular Structure and Molecular Nutrition, Ministry of Agriculture Strategic Research Chair Program (SRP, University of Saskatchewan) was applied in this study. The fractionation, predicted biodegradation and biodigestion were evaluated using the Cornell Net Carbohydrate Protein System. The results show that: (1) The steam flaking induced significant changes in CHO subfractions, CHO biodegradation and biodigestion in ruminant system. There were significant differences between non-processed (raw) and steam flaked grain corn (P<.01); (2) The ATR-Ft/VMS molecular technique was able to detect the processing induced CHO molecular structure changes; (3) Induced CHO molecular structure spectral features are significantly correlated (P<.05) to CHO subfractions, CHO biodegradation and biodigestion and could be applied to potentially predict CHO biodegradation (R2=0.87, RSD=0.74, P<.01) and intestinal digestible undegraded CHO (R2=0.87, RSD=0.24, P<.01). In summary, the processing induced molecular CHO structure changes in grain corn could be revealed by the ATR-Ft/VMS vibrational molecular spectroscopy. These molecular structure changes in grain were potentially associated with CHO biodegradation and biodigestion.

Near-Infrared Probe Based on Rhodamine Derivative for Highly Sensitive and Selective Lysosomal pH Tracking.

The development of near-infrared fluorescent probes with low pKa, high selectivity, high photostability, and high sensitivity for lysosomal pH detection is of great importance. In the present work, we developed a novel near-infrared lysosomal pH probe (Lyso-hNR) based on a rhodamine derivative. Lyso-hNR showed fast, highly sensitive, and highly selective fluorescence response to acidic pH caused by the H+-induced structure changes from the nonfluorescent spirolactam form to the highly emissive open-ring form. Lyso-hNR displays a significant fluorescence enhancement at 650 nm (over 280-fold) from pH 7.0 to 4.0 with a pKa value of 5.04. Live cell imaging data revealed that Lyso-hNR can selectively monitor lysosomal pH changes with excellent photostability and low cytotoxicity. In addition, Lyso-hNR can be successfully used in tracking lysosomal pH changes induced by chloroquine and those during apoptosis. All these features render Lyso-hNR a promising candidate to investigate lysosome-associated physiological and pathological processes.

Disconnect between alcohol-induced alterations in chromatin structure and gene transcription in a mouse embryonic stem cell model of exposure.

Alterations to chromatin structure induced by environmental insults have become an attractive explanation for the persistence of exposure effects into subsequent life stages. However, a growing body of work examining the epigenetic impact that alcohol and other drugs of abuse exert consistently notes a disconnection between induced changes in chromatin structure and patterns of gene transcription. Thus, an important question is whether perturbations in the 'histone code' induced by prenatal exposures to alcohol implicitly subvert gene expression, or whether the hierarchy of cellular signaling networks driving development is such that they retain control over the transcriptional program. To address this question, we examined the impact of ethanol exposure in mouse embryonic stem cells cultured under 2i conditions, where the transcriptional program is rigidly enforced through the use of small molecule inhibitors. We find that ethanol-induced changes in post-translational histone modifications are dose-dependent, unique to the chromatin modification under investigation, and that the extent and direction of the change differ between the period of exposure and the recovery phase. Similar to invivo models, we find post-translational modifications affecting histone 3 lysine 9 are the most profoundly impacted, with the signature of exposure persisting long after alcohol has been removed. These changes in chromatin structure associate with dose-dependent alterations in the levels of transcripts encoding Dnmt1, Uhrf1, Tet1, Tet2, Tet3, and Polycomb complex members Eed and Ezh2. However, in this model, ethanol-induced changes to the chromatin template do not consistently associate with changes in gene transcription, impede the process of differentiation, or affect the acquisition of monoallelic patterns of expression for the imprinted gene Igf2R. These findings question the inferred universal relevance of epigenetic changes induced by drugs of abuse and suggest that changes in chromatin structure cannot unequivocally explain dysgenesis in isolation.