Intermittent Regime Research Articles

Intermittent flow regimes near the convection threshold in ferromagnetic nanofluids.

The onset and decay of convection in a spherical cavity filled with ferromagnetic nanofluid and heated from below are investigated experimentally. It is found that, unlike in a single-component Newtonian fluid where stationary convection sets in as a result of supercritical bifurcation and where convection intensity increases continuously with the degree of supercriticality, convection in a multicomponent ferromagnetic nanofluid starts abruptly and has an oscillatory nature. The hysteresis is observed in the transition between conduction and convection states. In moderately supercritical regimes, the arising fluid motion observed at a fixed temperature difference intermittently transitions from quasiharmonic to essentially irregular oscillations that are followed by periods of a quasistationary convection. The observed oscillations are shown to result from the precession of the axis of a convection vortex in the equatorial plane. When the vertical temperature difference exceeds the convection onset value by a factor of 2.5, the initially oscillatory convection settles to a steady-state regime with no intermittent behavior detected afterward. The performed wavelet and Fourier analyses of thermocouple readings indicate the presence of various oscillatory modes with characteristic periods ranging from one hour to several days.

Deformation, Orientation and Bursting of Microcapsules in Simple Shear Flow: Wrinkling Processes, Tumbling and Swinging Motions

In a series of experiments we systematically investigated the orientation and deformation behavior of non-spherical capsules in simple shear flow. We observed a continuous capsule rotation at low shear rates, denoted as tumbling mode. A swinging mode at elevated shear rates was characterized by oscillations of the inclination angle around positive values, superimposed by a tank-treading motion of the capsule membrane. The transition between these different modes occurred via an intermittent regime. It turned out that the capsule deformation greatly influenced the orientation dynamics. In several experiments, we also observed shear-induced membrane wrinkling processes.

Fluid dynamic analysis of a continuous stirred tank reactor for technical optimization of wastewater digestion

Continuous stirred tank reactors (CSTR) are widely used in wastewater treatment plants to reduce the organic matter and microorganism present in sludge by anaerobic digestion. The present study carries out a numerical analysis of the fluid dynamic behaviour of a CSTR in order to optimize the process energetically. The characterization of the sludge flow inside the digester tank, the residence time distribution and the active volume of the reactor under different criteria are determined. The effects of design and power of the mixing system on the active volume of the CSTR are analyzed. The numerical model is solved under non-steady conditions by examining the evolution of the flow during the stop and restart of the mixing system. An intermittent regime of the mixing system, which kept the active volume between 94% and 99%, is achieved. The results obtained can lead to the eventual energy optimization of the mixing system of the CSTR.

Modeling shallow water table dynamics under subsurface irrigation and drainage

We develop conceptual and numerical models of water table dynamics under a subsurface irrigation and drainage system. The numerical model is implemented with distinct drainable and fillable porosity parameters that are estimated by accounting for the unsaturated zone fluxes to and from the shallow water table. The model was applied to two field sites under subsurface irrigation and drainage system in northeast Florida to simulate water table dynamics during potato growing seasons in 2010 and 2011. Simulated water table elevations showed a close agreement with the observed water table dynamics in the fields during both growing seasons. Furrows that act as shallow drains in the field facilitated rapid drawdown of the water table after rainfall events, while the outer, deeper ditches provided little drainage of water from the root-zone. Intermittent irrigation regimes, although could substantially reduce surface runoff from the fields, resulted in relatively deeper water tables during the growing season, suggesting a potential trade-off between water deliveries and root-zone soil moisture availability.

A simplified calculation of the intermittent periodic operating regime of an electromagnetic impact drive

This paper considers an intermittent periodic operating regime of an electromagnetic cyclic impact drive, in which the power fed from the supply source can substantially exceed that in its continuous operating regime. These investigations are important because of the need to improve the methods of designing electromagnetic impact drives characterized by various operating regimes in 10-min operating cycles and various cooling conditions during on and off periods. Calculations are carried out on the basis of the solution of Newton’s law of a heating equation for the maximum overheating for any nth cycle on the assumption that the electric drive is a homogeneous body with a uniformly distributed heat source, ideal heat conductivity, and constant heat generation rate. For a given operating regime, approximate expressions are obtained for the impact energy and frequency permissible from the standpoint of maximum heating conditions, depending on the thermophysical and geometrical parameters of the electric drive and allowing for various conditions of its cooling during on and off periods. An example is presented of a simplified calculation of the useful impact power of an electromagnetic impact drive for various cooling conditions and operating regimes.

On-and-off dynamics of a creeping frictional system.

We report on the dynamics of a model frictional system submitted to minute external perturbations. The system consists of a chain of sliders connected through elastic springs that rest on an incline. By introducing cyclic expansions and contractions of the rest length of the springs, we induce the reptation of the chain. Decreasing the amplitude of the perturbation below a critical value, we observe an intermittent creep regime characterized by alternated periods of reptation (flowing state) and rest (quiescent state). A further decrease of the perturbation leads to the disappearance of the reptation. The width of the transition region between the continuous creep and the full stop (i.e., the range of excitation amplitudes where the intermittent creep is observed) is shown to depend on the difference between the static (μ(s)) and the dynamic (μ(d)) friction coefficients. For μ(s) = μ(d) the intermittent creep is not observed. Studying the statistical features of the intermittent creep regime for any given perturbation amplitude, we find that the time the system resides in each state (flowing or quiescent) suggests that: i) reptation events are uncorrelated, and ii) rest events are history dependent. We show that this latter history dependence is consistent with the aging of the stress state inside the chain of sliders during the quiescent periods.

Dynamics of a multi-thermal loop in the solar corona

Context. We present an observation of a long-living multi-thermal coronal loop, visible in different extreme ultra-violet wavebands of SDO/AIA in a quiet-Sun region close to the western solar limb. Aims. Analysis of persistent kink displacements of the loop seen in different bandpasses that correspond to different temperatures of the plasma allows sub-resolution structuring of the loop to be revealed. Methods. A vertically oriented slit is taken at the loop top, and time-distance maps are made from it. Loop displacements in time-distance maps are automatically tracked with the Gaussian fitting technique and fitted with a sinusoidal function that is “guessed”. Wavelet transforms are further used in order to quantify the periodicity variation in time of the kink oscillations. Results. The loop strands are found to oscillate with the periods ranging between 3 and 15 min. The oscillations are observed in intermittent regime with temporal changes in the period and amplitude. The oscillations are different at three analysed wavelengths. Conclusions. This finding suggests that the loop-like threads seen at different wavelengths are not co-spatial, hence that the loop consists of several multi-thermal strands. The detected irregularity of the oscillations can be associated with a stochastic driver acting at the footpoints of the loop.

Impact of agricultural practices, elevated temperature and atmospheric carbon dioxide concentration on nitrogen and pH dynamics in soil and floodwater during the seasonal rice growth in Portugal

Data on the movements of available N and non-exchangeable NH4+ in the soil are of crucial importance in designing an efficient plant N nutrition management scheme in paddy rice fields. To investigate the processes affecting the dynamics of N and pH under Mediterranean conditions, rice (Oryza sativa L. cv. Ariete) was cultivated in 2011 and 2012 in Salvaterra de Magos (central Portugal) under the following climate scenarios: (i) ambient temperature and ambient [CO2] in the open-field, (ii) elevated temperature (+3°C) and ambient [CO2] in open-top chambers, and (iii) elevated temperature (+3°C) and elevated [CO2] (+175μmolmol−1) in open-top chambers. Plants were grown under an intermittent flooding regime. Soil and water samples were taken at eight different stages of plant growth, including before and after N basal and topdressing. Our study indicated that the processes underlying N changes in response to the timing of N fertilization were different depending on the N form. After basal dressing under aerobic conditions, both available and non-exchangeable NH4+ contents were increased. Following the topdressing under flooded conditions, the available content of soil N increased, whereas the non-exchangeable NH4+ content decreased. A negative relationship was found between soil pH and NH4+ “fixation” when roots were active, and vice-versa. Elevated temperature alone or in combination with elevated [CO2] had no effect on the total available N content in the soil and floodwater. Under elevated temperature, however, the non-exchangeable NH4+ content was significantly reduced (11%), with the same magnitude of change (10%) observed under co-elevation of temperature and [CO2]. These results suggested that non-exchangeable NH4+ in paddy fields might be insensitive to [CO2] elevation under Mediterranean conditions, while reductions observed under co-elevation of [CO2] and temperature might be associated with temperature alone. This information could be used to alter rice management practices and to adjust N application under climate change.

Two-phase flow pattern and pressure drop in silicon multi-microchannel with expansion–constriction cross-section

Gas–liquid two-phase intermittent flow pattern and frictional pressure drop in new silicon multi-microchannel were investigated experimentally by means of the IDT high-speed camera mounted together with a Nikon microscope. Each test section consisted of 10 parallel microchannels with 0.1mm wide and 0.2mm deep in constant cross-section segment and each microchannel consisted of an array of periodic reentrant cavities. The major two-phase flow pattern observed was intermittent in the test sections, and the intermittent sub regimes in the new microchannels were different from those displayed in the rectangular straight microchannel. Using nitrogen and deionized water as working fluids, the intermittent sub regime maps for the new multi-microchannel were obtained. Meanwhile, the pressure drops were compared with several existing correlations based on the homogeneous or separated mixture assumption. Results show that the homogeneous flow model cannot predict the two-phase pressure drop data well, while the separated flow model is proposed to provide a better prediction of the two-phase frictional pressure drop. Among the separated flow models investigated, the best two correlations of C value can provide mean deviations within less than 16% for all the three microchannels and all the predictions lie in the bound of ±30%.

Surface energy flux measurements in a flooded and an aerobic rice field using a single eddy-covariance system

About 90 % of the global rice production takes place in Asia, while European production is quantitatively modest. Italy is the Europe’s leading producer, with over half of total production concentrated in a large, traditional paddy rice area in the north of the country. High irrigation requirement for continuous flooding encourages the adoption of water saving techniques. In 2013, an intense monitoring activity was conducted on two fields characterized by continuous flooding and intermittent irrigation regimes, with the aim of comparing their agronomical and hydrological effects, including their influence on the energy balance. An eddy covariance station was installed on the levee between the two fields, to monitor latent (LE) and sensible (H) heat fluxes as a function of wind direction. Additionally, the fields were instrumented with net radiometers, soil heat flux (G) plates, thermistors, tensiometers, and multilevel moisture probes. Three footprint models were applied to determine position and size of the footprint area at each monitoring time step, providing similar results. Two half-hourly turbulent fluxes datasets were obtained, one for each irrigation regime, each one comprising about 10 % of the daytime time steps over the agricultural season. The reliability of the monitoring performed with a single EC station was confirmed by the energy balance closure (H + LE versus Rn-G), showing an imbalance lower than 10 % for both the regimes. A detailed analysis of the effect of the storage terms on the ground heat flux estimation and a more thorough analysis of the radiation balance for the two plots were also performed.

Investigating mode competition and three-dimensional features from two-dimensional velocity fields in an open cavity flow by modal decompositions

Shear-layer driven open cavity flows are known to exhibit strong self-sustained oscillations of the shear-layer. Over some range of the control parameters, a competition between two modes of oscillations of the shear layer can occur. We apply both Proper Orthogonal Decomposition and Dynamic Mode Decomposition to experimental two-dimensional two-components time and spaced velocity fields of an incompressible open cavity flow, in a regime of mode competition. We show that, although proper orthogonal decomposition successes in identifying salient features of the flow, it fails at identifying the spatial coherent structures associated with dominant frequencies of the shear-layer oscillations. On the contrary, we show that, as dynamic mode decomposition is devoted to identify spatial coherent structures associated with clearly defined frequency channels, it is well suited for investigating coherent structures in intermittent regimes. We consider the velocity divergence field, in order to identify spanwise coherent features of the flow. Finally, we show that both coherent structures in the inner-flow and in the shear-layer exhibit strong spanwise velocity gradients, and are therefore three-dimensional.

The ecology of rivers with contrasting flow regimes: identifying indicators for setting environmental flows

Summary The scientific basis for setting environmental flows is still hampered by our incomplete understanding of flow–ecology relationships and how river ecology varies with flow regime. We conducted a study of six rivers in Tasmania (Australia), three perennial and three intermittent, measuring a range of abiotic, biotic and ecosystem process attributes over 2 years. Our intentions were to identify: (i) whether they had an ecology characteristic of their flow regime and (ii) whether certain ecological attributes were more responsive to flow regime than others, and therefore represented candidate indicators (for environmental flows or flow alteration) specific to each flow regime. Only a few abiotic variables showed any relationship with flow regime: banks were higher, pools shallower and sediments finer in perennial rivers, and water temperature was generally lower in perennial rivers. Although rarely measured, we found that productivity and net ecosystem metabolism were strongly related to flow regime, whereas food chain length did not vary between perennial and intermittent rivers. Multivariate, rather than univariate, metrics of biotic assemblages were more effective at distinguishing perennial and intermittent flow regimes, and this was consistent among riparian and instream vegetation, biofilm and macroinvertebrate assemblages. In contrast to expectations from the literature, fish assemblages were not strong indicators of flow regime, largely due to the relatively low diversity and abundance of the Tasmanian fish fauna. Our findings demonstrate that rivers with different flow regimes can support a distinctive ecology, and conventional metrics of ecological character may not be the most sensitive to flow regime. We provide a set of ecological attributes that can: (i) support extrapolation of flow–ecology relationships across rivers to regional scales, (ii) provide benchmarks for environmental flow and flow restoration objectives, (iii) indicate alterations to natural or existing flow regimes and (iv) be used to monitor and evaluate flow management actions.

Ventilation strategies and indoor particulate matter in a classroom.

Particle mass and number concentrations were measured in a mechanically ventilated classroom as part of a study of ventilation strategies for energy conservation. The ventilation system was operated either continuously, intermittently, or shut down during nights while it was on during workdays. It appears that the nighttime ventilation scheme is not important for indoor particle concentrations the following day if fans are operated to give five air exchanges in advance of the workday. The highest concentrations of PM10 were found during and after workdays and were due to human activity in the classroom. The average workday PM10 concentration was 14μg/m(3) , well below the WHO guideline values. The number concentration of particles with diameter <0.750μm was typically between 0.5×10(3) and 3.5×10(3) particle/cm(3) . These concentrations were largely independent of the occupants. Transient formation of small particles was observed when ventilation was shut down. Then remaining ozone reacted with terpenes emitted by indoor sources and gave up to 8×10(3) particle/cm(3) before formation stopped due to lack of ozone. The intermittent ventilation regime was found least favorable for the indoor air quality in the classroom.

Structures and Lagrangian statistics of the Taylor–Green dynamo

The evolution of a Taylor–Green forced magnetohydrodynamic system showing dynamo activity is analyzed via direct numerical simulations. The statistical properties of the velocity and magnetic fields in Eulerian and Lagrangian coordinates are found to change between the kinematic, nonlinear and saturated regime. Fluid element (tracer) trajectories change from chaotic quasi-isotropic (kinematic phase) to mean magnetic field aligned (saturated phase). The probability density functions (PDFs) of the magnetic field change from strongly non-Gaussian in the kinematic to quasi-Gaussian PDFs in the saturated regime so that their flatness give a precise handle on the definition of the limiting points of the three regimes. Also the statistics of the kinetic and magnetic fluctuations along fluid trajectories changes. All this goes along with a dramatic increase of the correlation time of the velocity and magnetic fields experienced by tracers, significantly exceeding one turbulent large-eddy turn-over time. A remarkable consequence is an intermittent scaling regime of the Lagrangian magnetic field structure functions at unusually long time scales.

An intermittent rocking platform for integrated expansion and differentiation of human pluripotent stem cells to cardiomyocytes in suspended microcarrier cultures

The development of novel platforms for large scale production of human embryonic stem cells (hESC) derived cardiomyocytes (CM) becomes more crucial as the demand for CMs in preclinical trials, high throughput cardio toxicity assays and future regenerative therapeutics rises. To this end, we have designed a microcarrier (MC) suspension agitated platform that integrates pluripotent hESC expansion followed by CM differentiation in a continuous, homogenous process.Hydrodynamic shear stresses applied during the hESC expansion and CM differentiation steps drastically reduced the capability of the cells to differentiate into CMs. Applying vigorous stirring during pluripotent hESC expansion on Cytodex 1 MC in spinner cultures resulted in low CM yields in the following differentiation step (cardiac troponin-T (cTnT): 22.83±2.56%; myosin heavy chain (MHC): 19.30±5.31%). Whereas the lower shear experienced in side to side rocker (wave type) platform resulted in higher CM yields (cTNT: 47.50±7.35%; MHC: 42.85±2.64%). The efficiency of CM differentiation is also affected by the hydrodynamic shear stress applied during the first 3days of the differentiation stage. Even low shear applied continuously by side to side rocker agitation resulted in very low CM differentiation efficiency (cTnT<5%; MHC<2%). Simply by applying intermittent agitation during these 3days followed by continuous agitation for the subsequent 9days, CM differentiation efficiency can be substantially increased (cTNT: 65.73±10.73%; MHC: 59.73±9.17%). These yields are 38.3% and 39.3% higher (for cTnT and MHC respectively) than static culture control.During the hESC expansion phase, cells grew on continuously agitated rocker platform as pluripotent cell/MC aggregates (166±88×105μm2) achieving a cell concentration of 3.74±0.55×106cells/mL (18.89±2.82 fold expansion) in 7days. These aggregates were further differentiated into CMs using a WNT modulation differentiation protocol for the subsequent 12days on a rocking platform with an intermittent agitation regime during the first 3days. Collectively, the integrated MC rocker platform produced 190.5±58.8×106 CMs per run (31.75±9.74 CM/hESC seeded). The robustness of the system was demonstrated by using 2 cells lines, hESC (HES-3) and human induced pluripotent stem cell (hiPSC) IMR-90. The CM/MC aggregates formed extensive sarcomeres that exhibited cross-striations confirming cardiac ontogeny. Functionality of the CMs was demonstrated by monitoring the effect of inotropic drug, Isoproterenol on beating frequency.In conclusion, we have developed a simple robust and scalable platform that integrates both hESC expansion and CM differentiation in one unit process which is capable of meeting the need for large amounts of CMs.

Intermittent aerosol delivery to the lungs during high-flow nasal cannula therapy.

Use of submicrometer particles combined with condensational growth techniques has been proposed to reduce drug losses within components of high-flow nasal cannula therapy systems and to enhance the dose reaching the lower respiratory tract. These methods have been evaluated using continuous inhalation flow rather than realistic inhalation/exhalation breathing cycles. The goal of this study was to evaluate in vitro aerosol drug delivery using condensational growth techniques during high-flow nasal cannula therapy using realistic breathing profiles and incorporating intermittent aerosol delivery techniques. A mixer-heater combined with a vibrating mesh nebulizer was used to generate a submicrometer aerosol using a formulation of 0.2% albuterol sulfate and 0.2% sodium chloride in water. Delivery efficiency of the aerosol for 1 min through a nasal cannula was considered using an intermittent delivery regime with aerosol being emitted for either the entire inhalation time (2 s) or half of the inhalation period (1 s) and compared with continuous delivery. The deposition of the aerosol was evaluated in the nasal delivery components (ventilator tubing and cannula) and an in vitro adult nose-mouth-throat (NMT) model using 3 realistic breathing profiles. Significant improvements in dose delivered to the exit of the NMT model (ex-NMT) were observed for both condensational growth methods using intermittent aerosol delivery compared with continuous delivery, and increasing the tidal volume was found useful. The combination of the largest tidal volume with the shortest intermittent delivery time resulted in the lowest respiration losses and the highest ex-NMT delivered dose. Intermittent aerosol delivery using realistic breathing profiles of submicrometer condensational growth aerosols was found to be efficient in delivering nasally administered drugs in an in vitro airway model.

A novel implantable catheter system with transcutaneous port for intermittent convection-enhanced delivery of carboplatin for recurrent glioblastoma

Context: Inadequate penetration of the blood–brain barrier (BBB) by systemically administered chemotherapies including carboplatin is implicated in their failure to improve prognosis for patients with glioblastoma. Convection-enhanced delivery (CED) of carboplatin has the potential to improve outcomes by facilitating bypass of the BBB.Objective: We report the first use of an implantable CED system incorporating a novel transcutaneous bone-anchored port (TBAP) for intermittent CED of carboplatin in a patient with recurrent glioblastoma.Materials and methods: The CED catheter system was implanted using a robot-assisted surgical method. Catheter targeting accuracy was verified by performing intra-operative O-arm imaging. The TBAP was implanted using a skin-flap dermatome technique modeled on bone-anchored hearing aid surgery. Repeated infusions were performed by attaching a needle administration set to the TBAP. Drug distribution was monitored with serial real-time T2-weighted magnetic resonance imaging (MRI).Results: All catheters were implanted to within 1.5 mm of their planned target. Intermittent infusions of carboplatin were performed on three consecutive days and repeated after one month without the need for further surgical intervention. Infused volumes of 27.9 ml per day were well tolerated, with the exception of a single seizure episode. Follow-up MRI at eight weeks demonstrated a significant reduction in the volume of tumor enhancement from 42.6 ml to 24.6 ml, and was associated with stability of the patient’s clinical condition.Conclusion: Reduction in the volume of tumor enhancement indicates that intermittent CED of carboplatin has the potential to improve outcomes in glioblastoma. The novel technology described in this report make intermittent CED infusion regimes an achievable treatment strategy.

Evolution of the rainfall regime in the United Arab Emirates

Arid and semiarid climates occupy more than 1/4 of the land surface of our planet, and are characterized by a strongly intermittent hydrologic regime, posing a major threat to the development of these regions. Despite this fact, a limited number of studies have focused on the climatic dynamics of precipitation in desert environments, assuming the rainfall input – and their temporal trends – as marginal compared with the evaporative component. Rainfall series at four meteorological stations in the United Arab Emirates (UAE) were analyzed for assessment of trends and detection of change points. The considered variables were total annual, seasonal and monthly rainfall; annual, seasonal and monthly maximum rainfall; and the number of rainy days per year, season and month. For the assessment of the significance of trends, the modified Mann–Kendall test and Theil-Sen’s test were applied. Results show that most annual series present decreasing trends, although not statistically significant at the 5% level. The analysis of monthly time series reveals strong decreasing trends mainly occurring in February and March. Many trends for these months are statistically significant at the 10% level and some trends are significant at the 5% level. These two months account for most of the total annual rainfall in the UAE. To investigate the presence of sudden changes in rainfall time-series, the cumulative sum method and a Bayesian multiple change point detection procedure were applied to annual rainfall series. Results indicate that a change point happened around 1999 at all stations. Analyses were performed to evaluate the evolution of characteristics before and after 1999. Student’s t-test and Levene’s test were applied to determine if a change in the mean and/or in the variance occurred at the change point. Results show that a decreasing shift in the mean has occurred in the total annual rainfall and the number of rainy days at all four stations, and that the variance has decreased for the total annual rainfall at two stations. Frequency analysis was also performed on data before and after the change point. Results show that rainfall quantile values are significantly lower after 1999. The change point around the year 1999 is linked to various global climate indices. It is observed that the change of phase of the Southern Oscillation Index (SOI) has strong impact over the UAE precipitation. A brief discussion is presented on dynamical basis, the teleconnections connecting the SOI and the change in precipitation regime in the UAE around the year 1999.

Direct numerical simulations of two-phase immiscible wakes

Tammisola et al (2012 J. Fluid Mech. 713 632–58) have observed a counter-intuitive destabilizing effect of the surface tension in planar wakes by means of a global linear analysis. In the present study, we conduct direct numerical simulation (DNS) of wakes of two immiscible fluids. The numerical scheme is based on a level set approach to track the interface position. We simulate both sinuous and varicose perturbations of wake flows. DNS confirms a destabilization on the sinuous perturbations in presence of a moderate amount of the surface tension, while wakes are stabilized when the surface tension is further increased. Varicose perturbations present in contrast an intermittent low-amplitude oscillatory regime which does not significantly affect the position of the interface.

Effects of different ethanol-administration regimes on mRNA and protein levels of steroid 5α-reductase isozymes in prefrontal cortex of adolescent male rats

Underage drinking is a leading public health problem in developed countries. An increasing proportion of adolescents consume alcoholic beverages every weekend. Increased anxiety, irritability, and depression among adolescents may induce them to seek for the anxiolytic and rewarding properties of alcohol. Allopregnanolone (AlloP) shares rewarding effects of ethanol and modulates ethanol intake. The rate-limiting enzyme in the biosynthesis of AlloP is steroid 5α-reductase (5α-R), which is expressed as three isozymes, 5α-R1, 5α-R2, and 5α-R3. The objective of this study was to quantify the expression levels of 5α-R isozymes in prefrontal cortex (PFC) of adolescent male rats after three different regimes of ethanol administration. Adolescent male Wistar rats were administered with ethanol (4 g/kg) or saline intraperitoneally for 1 day (acute), for 7 days (chronic), or every 72 h for 14 days (chronic intermittent). Messenger (m)RNA and protein levels of 5α-R isozymes were measured by quantitative RT-PCR and Western blot, respectively. Ethanol significantly increased mRNA and protein levels of 5α-R1, 5α-R2, and 5α-R3 in the three different regimes of ethanol administration, being higher in the chronic intermittent regime in comparison with the others. The expression of the AlloP-biosynthetic enzyme 5α-Rs increases in the prefrontal cortex of adolescent male rats under acute, chronic, and chronic intermittent regime of ethanol administration. The latter is very interesting because it mimics the teenage drinking behavior.