Chromatin is generally classified as euchromatin or heterochromatin, each with distinct histone modifications, compaction levels, and gene expression patterns. Although the proper formation of ...heterochromatin is essential for maintaining genome integrity and regulating gene expression, heterochromatin can also spread into neighboring regions in a sequence-independent manner, leading to the inactivation of genes. Because the distance of heterochromatin spreading is stochastic, the formation of boundaries, which block the spreading of heterochromatin, is critical for maintaining stable gene expression patterns. Here we review the current understanding of the mechanisms underlying heterochromatin spreading and boundary formation.
A method for modeling piezoelectric-based ultrasonic acoustic–electric power and data transmission channels is presented. These channels employ piezoelectric disk transducers to convey signals across ...a series of physical layers using ultrasonic waves. This model decomposes the mechanical pathway of the signal into individual ultrasonic propagation layers which are generally independent of the layer׳s adjacent domains. Each layer is represented by a two-by-two traveling pressure wave transfer matrix which relates the forward and reverse pressure waves on one side of the layer to the pressure waves on the opposite face, where each face is assumed to be in contact with a domain of arbitrary reference acoustic impedance. A rigorous implementation of ultrasonic beam spreading is introduced and implemented within applicable domains. Compatible pressure-wave models for piezoelectric transducers are given, which relate the electric voltage and current interface of the transducer to the pressure waves on one mechanical interface while also allowing for passive acoustic loading of the secondary mechanical interface. It is also shown that the piezoelectric model׳s electrical interface is compatible with transmission line parameters (ABCD-parameters), allowing for connection of electronic components and networks. The model is shown to be capable of reproducing the behavior of realistic physical channels.
This paper presents a system capable of simultaneous high-power and high-data-rate transmission through solid metal barriers using ultrasound. By coaxially aligning a pair of piezoelectric ...transducers on opposite sides of a metal wall and acoustically coupling them to the barrier, an acoustic-electric transmission channel is formed which prevents the need for physical penetration. Independent data and power channels are utilized, but they are only separated by 25.4 mm to reduce the system's form factor. Commercial off-the-shelf components and evaluation boards are used to create realtime prototype hardware and the full system is capable of transmitting data at 17.37 Mbps and delivering 50 W of power through a 63.5-mm thick steel wall. A synchronous multi-carrier communication scheme (OFDM) is used to achieve a very high spectral efficiency and to ensure that there is only minor interference between the power and data channels. Also presented is a discussion of potential enhancements that could be made to greatly improve the power and data-rate capabilities of the system. This system could have a tremendous impact on improving safety and preserving structural integrity in many military applications (submarines, surface ships, unmanned undersea vehicles, armored vehicles, planes, etc.) as well as in a wide range of commercial, industrial, and nuclear systems.
This paper presents a method for two-way ultrasonic communication and power delivery through thick metallic enclosures without physical penetration. Acousticelectric channels are implemented using a ...pair of coaxially aligned piezoelectric transducers having 25.4 mm diameters and 1 MHz nominal resonant frequencies, mounted on steel walls having lengths in the range of 57.15 to 304.8 mm. A protocol is described which uses ultrasonic waves to achieve simultaneous bidirectional communication through the metallic enclosures. It is shown that such channels are very frequency selective, and a carrier frequency selection and tracking algorithm is presented to choose a frequency of operation at which both adequate power delivery and reliable full-duplex communication are achieved. Using this algorithm, sufficient power is harvested to allow for the continuous operation of internal electronics which require an aggregate of less than 100 mW. Reliable communication of sensor data is achieved at rates in excess of 30 kbps.
Treatment of postinflammatory hyperpigmentation in patients of Fitzpatrick skin types IV, V, and VI is difficult. Glycolic acid peels are useful for pigment dyschromias in caucasians; however, there ...are no controlled studies examining their safety and efficacy in dark-complexioned individuals.
To determine if serial glycolic acid peels provide additional improvement when compared with a topical regimen of hydroquinone and tretinoin.
Nineteen patients with Fitzpatrick skin type IV, V, or VI were randomized to a control or peel group. The control group applied 2% hydroquinone/10% glycolic acid gel twice daily and 0.05% tretinoin cream at night. The peel patients used the same topical regimen and, in addition, received six serial glycolic acid peels (68% maximum concentration). Patients were evaluated with photography, colorimetry, and subjectively.
Sixteen patients completed the study. Both treatment groups demonstrated improvement, but the patients receiving the glycolic acid peels showed a trend toward more rapid and greater improvement. The peel group also experienced increased lightening of the normal skin.
This pilot study demonstrates that serial glycolic acid peels provide an additional benefit, with minimal adverse effects, for the treatment of postinflammatory hyperpigmentation in dark-complexioned individuals.
The linear propagation of electromagnetic and dilatational waves through a sandwiched plate piezoelectric transformer (SPPT)-based acoustic-electric transmission channel is modeled using the transfer ...matrix method with mixed domain two-port ABCD parameters. This SPPT structure is of great interest because it has been explored in recent years as a mechanism for wireless transmission of electrical signals through solid metallic barriers using ultrasound. The model we present is developed to allow for accurate channel performance prediction while greatly reducing the computational complexity associated with 2- and 3-dimensional finite element analysis. As a result, the model primarily considers 1-dimensional wave propagation; however, approximate solutions for higher-dimensional phenomena (e.g., diffraction in the SPPT's metallic core layer) are also incorporated. The model is then assessed by comparing it to the measured wideband frequency response of a physical SPPT-based channel from our previous work. Very strong agreement between the modeled and measured data is observed, confirming the accuracy and utility of the presented model.
Previous studies have shown only modest correlation between multiple sclerosis (MS) lesions on MRI and clinical disability.
To investigate the relationship between proton density/T2-weighted (T2) ...burden of disease (BOD) quantitatively measured on MRI scans and clinical determinants including disability.
Using the Sylvia Lawry Centre for Multiple Sclerosis Research (SLCMSR) database, the authors studied baseline T2 BOD data from a pooled subsample of 1,312 placebo MS patients from 11 randomized controlled trials. Univariate comparisons guided development of multiple regression models incorporating the most important clinical predictors.
Significant, although weak to moderate, correlations were found between T2 BOD and age at disease onset, disease duration, disease course, disability (as measured by the Expanded Disability Status Scale EDSS), relapse rate, certain presenting symptoms, and gadolinium enhancement. An unexpected but key finding that persisted in the multiple regression analyses was a plateauing relationship between T2 BOD and disability for EDSS values above 4.5.
This study confirmed the limited correlation between clinical manifestations and T2 burden of disease (BOD) but revealed an important plateauing relationship between T2 BOD and disability.
Computer simulations were used to evaluate the ISIS localization technique as implemented with both head and surface coils. The effects of chemical shift, B1 inhomogeneity, repetition time, T2 ...relaxation, a postacquisition saturation pulse, and a B1 insensitive observation pulse were examined. Integrals of ISIS signals over the sample volume showed that significant signal loss from the volume of interest (VOI) and contamination from outside the VOI can occur for both head and surface coil ISIS experiments. The results showed that the saturation pulse, order of the various ISIS acquisitions, and repetition time affect contamination but not signal loss. In addition, short T2 and high RF power can combine synergistically to degrade the selective inversion pulses, causing further contamination and signal loss.
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