Stabilizing complex-Langevin field-theoretic simulations for block copolymer melts.

Complex-Langevin field-theoretic simulations (CL-FTSs) provide an approximation-free method of calculating fluctuation corrections to the self-consistent field theory (SCFT) of block copolymer melts. However, the complex fields are prone to the formation of hot spots, which causes the method to fail. This problem has been attributed to an invariance under complex translations, which allows the system to drift away from the real-valued saddle-point of SCFT.

Bicontinuous microemulsion in binary blends of complementary diblock copolymers.

The phase behavior of binary blends of AB diblock copolymers of compositions f and 1 - f is examined using field-theoretic simulations. Highly asymmetric compositions (i.e.

Fluctuation-Corrected Phase Diagrams for Diblock Copolymer Melts.

New developments in field-theoretic simulations (FTSs) are used to evaluate fluctuation corrections to the self-consistent field theory of diblock copolymer melts. Conventional simulations have been limited to the order-disorder transition (ODT), whereas FTSs allow us to evaluate complete phase diagrams for a series of invariant polymerization indices. The fluctuations stabilize the disordered phase, which shifts the ODT to higher segregation.

Accounting for the ultraviolet divergence in field-theoretic simulations of block copolymer melts.

This study examines the ultraviolet (UV) divergence in field-theoretic simulations (FTSs) of block copolymer melts, which causes an unphysical dependence on the grid resolution, Δ, used to represent the fields. Our FTSs use the discrete Gaussian-chain model and a partial saddle-point approximation to enforce incompressibility. Previous work has demonstrated that the UV divergence can be accounted for by defining an effective interaction parameter, χ=zχ+cχ +cχ +⋯, in terms of the bare interaction parameter, χ, used in the FTSs, where the coefficients of the expansion are determined by a Morse calibration.

Well-tempered metadynamics applied to field-theoretic simulations of diblock copolymer melts.

Well-tempered metadynamics (WTMD) is applied to field-theoretic simulations (FTS) to locate the order-disorder transition (ODT) in incompressible melts of diblock copolymer with an invariant polymerization index of N̄=10. The polymers are modeled as discrete Gaussian chains with N = 90 monomers, and the incompressibility is treated by a partial saddle-point approximation. Our implementation of WTMD proves effective at locating the ODT of the lamellar and cylindrical regions, but it has difficulty with that of the spherical and gyroid regions.

Entropic surface segregation from athermal polymer blends: Polymer flexibility vs bulkiness.

We examine athermal binary blends composed of conformationally asymmetric polymers of equal molecular volume next to a surface of width ξ. The self-consistent field theory (SCFT) of Gaussian chains predicts that the more compact polymer with the shorter average end-to-end length, R, is entropically favored at the surface. Here, we extend the SCFT to worm-like chains with small persistence lengths, ℓ, relative to their contour lengths, ℓ, for which R≈2ℓℓ.

Field-Theoretic Simulations for Block Copolymer Melts Using the Partial Saddle-Point Approximation.

Field-theoretic simulations (FTS) provide an efficient technique for investigating fluctuation effects in block copolymer melts with numerous advantages over traditional particle-based simulations. For systems involving two components (i.e.

Fluctuation correction for the order-disorder transition of diblock copolymer melts.

The order-disorder transition (ODT) of diblock copolymer melts is evaluated for an invariant polymerization index of N¯=10, using field-theoretic simulations (FTS) supplemented by a partial saddle-point approximation for incompressibility. For computational efficiency, the FTS are performed using the discrete Gaussian-chain model, and results are then mapped onto the continuous model using a linear approximation for the Flory-Huggins χ parameter. Particular attention is paid to the complex phase window.

Instability of the Microemulsion Channel in Block Copolymer-Homopolymer Blends.

Field theoretic simulations are used to predict the equilibrium phase diagram of symmetric blends of AB diblock copolymer with A- and B-type homopolymers. Experiments generally observe a channel of bicontinuous microemulsion (BμE) separating the ordered lamellar (LAM) phase from coexisting homopolymer-rich (A+B) phases. However, our simulations find that the channel is unstable with respect to macrophase separation, in particular, A+B+BμE coexistence at high T and A+B+LAM coexistence at low T.

Adaptable Angled Stereotactic Approach for Versatile Neuroscience Techniques.

Stereotactic surgery is an essential tool in the modern neuroscience lab. However, the ability to precisely and accurately target difficult-to-reach brain regions still presents a challenge, particularly when targeting brain structures along the midline. These challenges include avoiding of the superior sagittal sinus and third ventricle and the ability to consistently target selective and discrete brain nuclei.

Field theoretic approach for block polymer melts: SCFT and FTS.

This perspective addresses the development of polymer field theory for predicting the equilibrium phase behavior of block polymer melts. The approach is tailored to the high-molecular-weight limit, where universality reduces all systems to the standard Gaussian chain model, an incompressible melt of elastic threads interacting by contact forces. Using mathematical identities, this particle-based version of the model is converted to an equivalent field-based version that depends on fields rather than particle coordinates.

Perineuronal Net Formation during the Critical Period for Neuronal Maturation in the Hypothalamic Arcuate Nucleus.

In leptin-deficient mice, obesity and diabetes are associated with abnormal development of neurocircuits in the hypothalamic arcuate nucleus (ARC), a critical brain area for energy and glucose homeostasis. As this developmental defect can be remedied by systemic leptin administration, but only if given before postnatal day 28, a critical period (CP) for leptin-dependent development of ARC neurocircuits has been proposed. In other brain areas, CP closure coincides with the appearance of perineuronal nets (PNNs), extracellular matrix specializations that restrict the plasticity of neurons that they enmesh.

Calibration of a lattice model for high-molecular-weight block copolymer melts.

The Morse calibration is applied to a lattice model designed for efficient simulations of two-component polymer melts of high molecular weight. The model allows multiple occupancy per site, which results in high invariant polymerization indices, and interactions are limited to monomers within the same site, which enhances the computational speed. The calibration maps the interaction parameter of the lattice model, α, onto the Flory-Huggins χ parameter of the standard Gaussian-chain model, by matching the disordered-state structure function, S(k), of symmetric diblock copolymers to renormalized one-loop predictions.

Calibration of the Flory-Huggins interaction parameter in field-theoretic simulations.

Field-theoretic simulations (FTS) offer a versatile method of dealing with complicated block copolymer systems, but unfortunately they struggle to cope with the level of fluctuations typical of experiments. Although the main obstacle, an ultraviolet divergence, can be removed by renormalizing the Flory-Huggins χ parameter, this only works for unrealistically large invariant polymerization indexes, N¯. Here, we circumvent the problem by applying the Morse calibration, where a nonlinear relationship between the bare χ used in FTS and the effective χ corresponding to the standard Gaussian-chain model is obtained by matching the disordered-state structure function, S(k), of symmetric diblock copolymers to renormalized one-loop predictions.

The Hypothalamic Arcuate Nucleus-Median Eminence Is a Target for Sustained Diabetes Remission Induced by Fibroblast Growth Factor 1.

In rodent models of type 2 diabetes (T2D), sustained remission of diabetic hyperglycemia can be induced by a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1). To identify the brain areas responsible for this effect, we first used immunohistochemistry to map the hypothalamic distribution of phosphorylated extracellular signal-related kinase 1/2 (pERK1/2), a marker of mitogen-activated protein kinase-ERK signal transduction downstream of FGF receptor activation. Twenty minutes after icv FGF1 injection in adult male Wistar rats, pERK1/2 staining was detected primarily in two hypothalamic areas: the arcuate nucleus-median eminence (ARC-ME) and the paraventricular nucleus (PVN).

Effect of chain stiffness on the entropic segregation of chain ends to the surface of a polymer melt.

Entropic segregation of chain ends to the surface of a monodisperse polymer melt and its effect on surface tension are examined using self-consistent field theory (SCFT). In order to assess the dependence on chain stiffness, the SCFT is solved for worm-like chains. Our focus is still on relatively flexible polymers, where the persistence length of the polymer, , is comparable to the width of the surface profile, , but still much smaller than the total contour length of the polymer, .

Glucoregulatory responses to hypothalamic preoptic area cooling.

Normal glucose homeostasis depends on the capacity of pancreatic β-cells to adjust insulin secretion in response to a change of tissue insulin sensitivity. In cold environments, for example, the dramatic increase of insulin sensitivity required to ensure a sufficient supply of glucose to thermogenic tissues is offset by a proportionate reduction of insulin secretion, such that overall glucose tolerance is preserved. That these cold-induced changes of insulin secretion and insulin sensitivity are dependent on sympathetic nervous system (SNS) outflow suggests a key role for thermoregulatory neurons in the hypothalamic preoptic area (POA) in this metabolic response.

Peripheral Mechanisms Mediating the Sustained Antidiabetic Action of FGF1 in the Brain.

We recently reported that in rodent models of type 2 diabetes (T2D), a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1) induces remission of hyperglycemia that is sustained for weeks. To clarify the peripheral mechanisms underlying this effect, we used the Zucker diabetic fatty / rat model of T2D, which, like human T2D, is characterized by progressive deterioration of pancreatic β-cell function after hyperglycemia onset. We report that although icv FGF1 injection delays the onset of β-cell dysfunction in these animals, it has no effect on either glucose-induced insulin secretion or insulin sensitivity.

Field-theoretic simulations of bottlebrush copolymers.

Traditional particle-based simulations struggle with large bottlebrush copolymers, consisting of many side chains grafted to a backbone. Field-theoretical simulations (FTS) allow us to overcome the computational demands in order to calculate their equilibrium behavior. We consider bottlebrushes where all grafts are symmetric diblock copolymers, focusing on the order-disorder transition (ODT) and the size of ordered domains.

Distinct Neuronal Projections From the Hypothalamic Ventromedial Nucleus Mediate Glycemic and Behavioral Effects.

The hypothalamic ventromedial nucleus (VMN) is implicated both in autonomic control of blood glucose and in behaviors including fear and aggression, but whether these divergent effects involve the same or distinct neuronal subsets and their projections is unknown. To address this question, we used an optogenetic approach to selectively activate the subset of VMN neurons that express neuronal nitric oxide synthase 1 (VMN neurons) implicated in glucose counterregulation. We found that photoactivation of these neurons elicits ) robust hyperglycemia achieved by activation of counterregulatory responses usually reserved for the physiological response to hypoglycemia and ) defensive immobility behavior.

Fluctuation effects in blends of A + B homopolymers with AB diblock copolymer.

Field-theoretic simulations (FTSs) are performed on ternary blends of A- and B-type homopolymers of polymerization N and symmetric AB diblock copolymers of polymerization N. Unlike previous studies, our FTSs are conducted in three-dimensional space, with the help of two new semi-grand canonical ensembles. Motivated by the first experiment to discover bicontinuous microemulsion (BμE) in the polyethylene-polyethylene propylene system, we consider molecules of high molecular weight with size ratios of α ≡ N/N = 0.