From a Poincar�� plot, two non-linear parameters SD1 and SD2 can

From a Poincar�� plot, two non-linear parameters SD1 and SD2 can be calculated [21]:SD1=12Var(xn+1?xx)(1)SD2=2SDNN2?12SD12(2)where selleck chem x represents the HHI or RRI sequences, symbol Var is the variance of the differences in successive RRI or HHI, SDNN is the standard deviation of the RRIs or HHIs. SD1 represents short Inhibitors,Modulators,Libraries term beat-to-beat variability of the data and SD2 is long term beat-to-beat variability.3.3. Statistical AnalysisTo assess how similar HRV parameters derived from heartbeat compared with those derived from the ECG, one-way ANOVA wa
The variation of viscoelastic properties of a polymer material during its crystallization is important information in the design of a variety of polymer processing equipments.

For instance, the property change has a key role in the design of a mold for an injection molding machine, but the property measurement is difficult while the polymer crystallizes.A quartz crystal resonator is composed of a thin quartz crystal sandwiched between two metal electrodes that establish an alternating Inhibitors,Modulators,Libraries electric field across the crystal, causing vibrational motion of the crystal. The motion is characterized with the resonant frequency and admittance of the resonator, and the characteristic is sensitive to the changes of mass and physical property of an overlayer on its electrode. Because the resonator is so sensitive, it can sense a variety of changes in micro-scale at the electrode interface. In polymerization, the rheological properties of a reactant and product mixture vary continuously as the polymerization Inhibitors,Modulators,Libraries proceeds.

The resonator has been implemented in the monitoring of a UV photopolymerization by measuring its resonant resistance [1]. The nucleation and crystal formation in a cooling crystallization have also been investigated Inhibitors,Modulators,Libraries with the quartz crystal resonator [2,3].The resonant frequency and admittance of the resonator can be interpreted to the changes of mass and viscoelasticity of an overlayer at its electrode interface. Reed et al. [4] presented a physical description of a viscoelastically loaded resonator for either very thick viscous fluids or very thin elastic overlayers. Buttry and Ward [5] gave an extensive review of the quart crystal resonator including basic principles of an AT-cut resonator and relation of the mechanical system composed of a spring, mass and a damper to the electrical circuit of resistance, inductance and capacitance.

Nwankwo and Durning [6] provided an impedance analysis of the resonator for very thick viscoelastic fluids. Kim et al. [7] demonstrated the applicability of a specially designed GSK-3 resonator system to monitor the change of viscoelastic property of thin polymer films selleck bio subjected to temperature variation. When a PMMA/PVAc blend was coated on the one side of the resonator, the resonant frequency decreased accompanying hysteresis with the increased temperature.

Energy balance-based category: in this class, the routing protoco

Energy balance-based category: in this class, the routing protocols are proposed from different points of view, but with a uniform objective which is energy balance. When a node is assigned some redundant and repetitive missions what has been assigned to other nodes, the node will consume energy disproportionally and become Inhibitors,Modulators,Libraries quickly useless. It appears that Inhibitors,Modulators,Libraries energy balance-based methods can also improve the energy efficiency of the sensor nodes.In the rema
Due to the benefits of low cost, rapid deployment, self-organization capability and cooperative data processing, wireless sensor networks (WSNs) have been proposed as a practical solution for a wide range of applications [1], such as battlefield surveillance, habitat monitoring, intelligent agriculture, home automation, etc.

A typical WSN is composed of a large number of sensor nodes responsible for sensing data and a sink node responsible for collecting and processing data. Since the energy supply for each sensor node is usually extremely limited, energy efficiency is the primary challenge Inhibitors,Modulators,Libraries of WSNs. Previous research works have indicated that a clustered structure [2,3] and multi-hop routing [4] are essential for better energy efficiency in large scale WSNs.In WSNs, the data traffic follows a many-to-one communication pattern. Nodes closer to the sink tend to carry heavier traffic loads, which will deplete their energy faster [5�C9]. Wadaa et al. [8] argued that by the time nodes closest to the sink deplete their energy, nodes farther away from the sink may still have up to 93% of their initial energy available, assuming all nodes have the same fixed transmission range and nodes are uniformly distributed in the network.

In the literature, this problem is referred as the energy hole problem and a number of studies have been conducted to mitigate its impact on the lifetime of a WSN, including energy-efficient clustering schemes [5,7,10], analysis of the energy hole problem [11,12], nonuniform node distribution strategies [13,14], and utilization of mobile nodes [15].In our previous Inhibitors,Modulators,Libraries work, a highly scalable network architecture, named Progressive Multi-hop Rotational Clustered (PMRC) structure [16], was proposed for the construction of large scale WSNs. Like other multi-hop structures, PMRC also suffers from the energy hole problem.

This issue was alleviated to some extent by the Overlapping Layers (OL) scheme [17], which tends to balance the relay load at the cluster Anacetrapib heads for all layers by overlapping the neighbor layers following a desired overlap range. However, due to the fixed layer boundary and range overlap, the network lifetime of OL-enabled WSN is still limited by those nodes which have exactly one candidate cluster head. To overcome this limit, the Minimum Overlapping Layers (MOL) scheme [18] was proposed to gradually increase the required minimum overlap between neighbor layers during network lifetime.

1 �� 0 8 m size with

1 �� 0.8 m size with this explanation a grid step of 0.1 m). We do not focus on the performance of the descriptor but in the parameters of the filter to optimize the localization process. We test in a variety of environments, from small ones to larger ones, Inhibitors,Modulators,Libraries with a maximu
When a device wishes to determine its position, it does two things. First, the hardware uses an antenna and receiver to capture and record a location measurement. Second, the location measurement is converted into a global position in the form of longitude and latitude. Most often these two steps are conflated, and both are seen as necessary to enable location-based applications. In this paper we argue that for many security applications only the first step is needed: there is no need to accurately map the location measurement to an accurate global position.

Therefore, these location-based security applications can be implemented using a variety of radio frequency (RF) signals, including broadcast communication signals, such as AM/FM, cellular, DTV, Wi-Fi, etc., navigation signals, and an integration of various signals.While GPS provides accurate position data, other location services are far less accurate. Inhibitors,Modulators,Libraries LOng RAnge Navigation (Loran) [1], for example, uses a 3 km wavelength, and standalone Inhibitors,Modulators,Libraries Loran has an absolute accuracy of several hundred meters. Loran-C, the most recent version of Loran in use, is a terrestrial navigation system originally designed for naval applications and its operation is described in Appendix A. Its modernized version, called enhanced Inhibitors,Modulators,Libraries Loran (eLoran) [2], together with differential corrections can achieve an accuracy of 8 to 20 meters.

This paper uses standalone Loran-C, which has good repeatable accuracy, but low absolute accuracy, as a case study and shows that high absolute accuracy is not a requirement for a number of location-based Entinostat security applications. As with all radio-based systems, Loran-C radio signals are distorted by buildings and other objects, causing measurements to change greatly over short distances. Our main result shows that one can exploit these chaotic changes to obtain a precise and reproducible location tag with an accuracy of about 20 meters. Reproducibility means that selleck chemicals llc measurements at the same location at different times always produce the same tag. While there is no way to map location measurements to an accurate position, there are still many applications, primarily security applications, for which a reproducible and precise tag is sufficient.We build a reproducible and precise tag using recent results from biometric authentication for location-based security applications. In particular, we rely on fuzzy extractors [3,4] and secure sketches [5,6], originally designed for fingerprint-based authentication.

In the following section the operation

In the following section the operation sellekchem principles of range imaging sensors based on PMD technology are briefly explained. Then, the geometric models are thoroughly described in Section Inhibitors,Modulators,Libraries 3. The details of calibration Inhibitors,Modulators,Libraries experiments including network and test field design are represented in Section 4. Section 5 reports the results of calibration method in terms of parameters accuracy and correlations, effectiveness of the systematic error models and noticeable impact of joint calibration with RBG camera. Finally, conclusions and future work are discussed in Section 6.2.?Range Imaging PrinciplesRange cameras based on PMD technology operate on the Time of Flight (ToF) concept to provide distance information. Typically, a PMD camera consists of a PMD chip and its peripheral electronics, emitter and receiver optics and Inhibitors,Modulators,Libraries other standard camera parts.
The emitter, which is an illumination source, emits near infrared light. The reflected light is then received to measure the distance to the object. In contrast to typical ToF devices, e.g., laser scanners, all pixels in the PMD array simultaneously analyze the received optical signal to measure the depths of the corresponding points in space. Inhibitors,Modulators,Libraries The PMD chip is based on CMOS technology, Dacomitinib which also provides an automatic suppression of background light, allowing the device to be utilized outdoor as well as indoor [24].In order to provide range information, a reference electrical signal is applied to the modulation gates of each pixel on PMD array. Additionally, the incident light on photo-gates of pixels generates a second signal.
The received optical signal differs from the reference one by a phase shift proportional to the depth of the reflecting target. To calculate the distance, the autocorrelation function of electrical and optical signal is analyzed by phase-shift algorithm (Figure 1). Using four samples A1, A2, A3 and A4 each shifted by 90 degrees the Alisertib phase shift, which is proportional to the distance, can be calculated using the following equation:��=arctan(A1?A3A2?A4)(1)Figure 1.Autocorrelation function, phase shift, amplitude and intensity.In addition to the phase shift, two other values are extracted; signal strength of the received signal (amplitude) and the offset b of the samples which represents the gray-scale value of each pixel (intensity):a=(A1?A3)2+(A2?A4)22(2)b=A1+A2+A3+A44(3)The distance d to the target is therefore given by Equation (4):d=c.��4��.

As a consequence, this design (a) allows for large rock samples t

As a consequence, this design (a) allows for large rock samples to be measured without weighing down the instrument-sphere connection, selleck Ruxolitinib (b) prevents lose material from falling into the sphere without the use of throughput-reducing window material and (c) allows for measuring soils in Petri dishes. When measuring soil samples in the near-infrared a typical setup is to place a Petri dish with soil material on a sample port at the top of the sphere and measure through the dish. Petri dishes are opaque in the TIR and thus cannot be penetrated by TIR radiation if placed on top of the sphere.2.1.2. Calibration DesignThe design of the sphere allows for two different calibration procedures: the substitution and comparative methods.
To calibrate by the substitution method, a reference material is first placed under the sample port and a reference measurement Inhibitors,Modulators,Libraries is taken. Then the reference is substituted by the sample and a sample measurement is taken. The reference and sample measurements Inhibitors,Modulators,Libraries are ratioed against each other to convert the spectrum to reflectance percentages.In the comparative method the sample is placed Inhibitors,Modulators,Libraries under the sample port and becomes an integral part of the sphere wall during the reference as well as sample Inhibitors,Modulators,Libraries measurements. To perform a reference measurement the folding mirror of the sphere can be rotated such that the incoming energy is deflected onto the gold-coated sphere wall instead of the sample (Figure 2). The sphere wall itself is used as the reference material. After the reference measurement, the folding mirror is rotated back and the sample in the sample port is measured.
The two spectra are ratioed to convert to Drug_discovery reflectance percentages. For long measurements we equipped the folding mirror lever with an electric motor (Figure 3). Through automated swapping, several reference and sample measurem
Autonomous Underwater Vehicles (AUVs) have portable energy and self-control ability which make them different from remote operate vehicles (ROVs). They are suitable for commercial and military tasks underwater, under-ice or in other environments [1,2]. In the past few decades, the world plans to build or has built about 200 AUVs, such as the well-known REMUS by WHOI [3] or MIT Sea Grant��s Odyssey [4]. As the applications of AUVs are spreading to deeper seas and longer distances, high accuracy navigation capability will play a vital role.
Inertial navigation systems (INS) are widely used in AUVs, but the navigation errors accumulate over time and waves and currents exacerbate this. Though the errors can be reduced periodically by using GPS, electromagnetic selleck chemical Oligomycin A signals decay very quickly in the water, so the navigation of underwater vehicles cannot rely on GPS. As acoustic signals decay extremely slowly in seawater, acoustic navigation is widely used in three ways: long baseline, short baseline, ultra short baseline.

The goals of previous 3D methods are more suitable for visualizat

The goals of previous 3D methods are more suitable for visualization on vessels 3D structure, although the quantification is also possible if vessel boundaries are obtained.To solve this problem, we propose a 3D-expansion of DP that can seek an optimal surface in a 3D matrix. This method can search succeeding boundaries selleck chemicals llc in Inhibitors,Modulators,Libraries an image sequence, as succeeding boundaries form a surface in a 3D matrix. The relationship between two succeeding boundaries is thus considered in the smoothness constraint. To investigate the performance of this method, we design experiments to Inhibitors,Modulators,Libraries calculate its accuracy. The significance of this paper is two-fold: (1) we propose a 3D-expansion of DP which can locate an optimal surface among a 3D matrix; (2) we explore the best parameter set of the proposed 3D expansion of DP for round shape objects’ boundary detection, and its unsigned relative error is reported.
The rest of this paper is organized as follows. In Sections 2 and 3, we introduce the 2D and 3D-expansion of DP, respectively. In Section Inhibitors,Modulators,Libraries 4, we address our experimental designs. In Section 5, we illustrate the experimental results. We then discuss the proposed method and give a conclusion in Sections 6 and 7.2.?Methods2.1. 2D Dynamic ProgrammingIn computer science, DP is a method for solving complex problems, which has similar properties that can be broken down into simpler sub-problems. Therefore, to solve Inhibitors,Modulators,Libraries a problem is then transformed to solve different parts of its sub-problems. However, many sub-problems are actually the same. The DP solves each sub-problem once and the result is saved for solving next similar sub-problem.
Thus AV-951 DP reduces the number of computations. A good tutorial on DP can be found in [14]. This approach was often used to find the contour of an object such as a road [15], and it has many applications on boundary detection in medical images [6,8�C10,16�C18]. A study has shown that DP outperforms some edge detectors against noise, including the Canny and Prewitt detector [19]. If the object to be detected contains noise, the DP might therefore be a good detection method, as for an MRI breast mass segmentation [20]. Similarly, DP is suitable for boundary detection in noisy images, including sonography [8,21] and MRI vessel segmentation without a contrast injection [10]. The 2D boundary detection using DP can be transformed to an optimization problem seeking an optimal path in a feature image.
The searching direction is performed from one side to its opposite side. Converting a closed contour from its center in the Cartesian coordinate to the polar coordinate is thus required [22] for closed contour detection.Let the feature image saved in a 2D matrix be F, F M��N. The boundary detection problem is then transformed to an optimization problem that selleck compound searches for an optimal path. Assume the searching direction is from left to right.

Tracer gas experiments are commonly conducted to calculate the ve

Tracer gas experiments are commonly conducted to calculate the ventilation rate from the difference between indoor and outdoor concentrations. The tracer full article gas method prefers the good mixing of tracer gas inside the building. For those buildings, imperfect mixing would lead to large uncertainty of the resulting ventilation rate measurements. It is very difficult to achieve in naturally ventilated buildings [5]. In this context, it is very important to Inhibitors,Modulators,Libraries find the optimal sampling position for the indoor concentrations.Thus, research is needed for decreasing the sampling positions and finding out the optimal regions in order to estimate the ventilation rate. Buggenhout et al. tested 36 indoor tracer gas sampling positions to find the optimal ones for the ventilation rate using the decay method.
They concluded that the measurement errors can be as large as 86% of the actual ventilation rate by choosing an improper sampling position. The outlet position which gave measurement errors below 10% was found to be optimal. Inhibitors,Modulators,Libraries This study was conducted in mechanically ventilated livestock buildings. Unfortunately, little literature can be referred to for determining the optimal sampling positions in naturally ventilated building [5]. The optimal sampling position of exhaust air in naturally ventilated buildings is very difficult to find, and involves large uncertainty. This is either because the air outlet of Inhibitors,Modulators,Libraries a natural ventilation system may shift with varied wind conditions and opening states, or the inlet and outlet can exist simultaneously at one opening [6�C8].
At present, measurement in such a building requires a lot of sampling positions and expensive multi-point measurements and it is very time consuming. A hypothesis is that the measured values at the optimal sampling positions are representatives for the mean value of the whole-field Inhibitors,Modulators,Libraries indoor concentration [9]. Hence, many scientists have measured several sampling positions inside the building and calculated the average to represent the indoor concentration [5,8]. Due to the non-perfect mixing, large uncertainty still lies in their methods [5].Another difficulty is that the optimal sampling positions may change location when the opening states are modified or the wind direction changes. This is a challenge for us when intending to measure the indoor concentration by using fewer sampling positions.
Therefore, it is necessary to determine the sampling positions independent of the opening states and wind directions.The objective Cilengitide of this study is to find the optimal sampling positions for ventilation rate measurement in a naturally ventilated building. In this research, we focused on the tracer gas measurement method. The investigation includes eight different cases, with four opening states and two wind directions in perpendicular or selleck kinase inhibitor oblique wind directions.

ontrast, the CP190dC protein is no longer present at the y locus

ontrast, the CP190dC protein is no longer present at the y locus of the y2 polytene chro mosome in the mod mutant. This result supports the idea that the interaction between the BTB domains of Cp190 and Mod 67. 2 contributes to the binding of Cp190 with the Su insulator complex. BTB domains often mediate dimers with other BTB containing selleckchem proteins, and thus we posit that the Cp190 BTB domain interacts with the Mod 67. 2 BTB domain and that Mod 67. 2 recruits Cp190 lacking the C terminal E rich domain. ChIP assays with homozygous CP190En15 pupae indi cate that CP190dC associates with all sites that bind wild type Cp190, because the signals of all tested sites were significantly higher than the 1A6 negative control region.

The signals Inhibitors,Modulators,Libraries at 1A2 and 62D were stronger Inhibitors,Modulators,Libraries than Fab 8, whereas in the wild type Cp190 ChIP results the signals at 1A2 and 62D were weaker than Fab 8. The result suggests that the C terminal E rich domain con tributes partially to the association of Cp190 with the CTCF complexes at Fab 8. The CP190dC protein associates with all Cp190 containing insulator complexes but the GFP CP190BTB nls does not. We thus reasoned that another part of the Cp190 protein in addition to the BTB domain must also be essential for the association. We noticed that there is a D Rich acidic region between the zinc fingers and the BTB domain. This D rich region is in the CP190dC protein, but not in the GFP CP190BTB Inhibitors,Modulators,Libraries nls protein. We generated flies carrying the P which encodes a Cp190 fragment containing both the BTB and the D rich domain.

GFP CP190BTB D pro tein localizes to polytene chromosomes as distinct bands and not to extra chromosomal spaces in living salivary glands. In addition, this GFP fusion protein co localized completely with the mRFP CP190 on poly tene chromosomes. Inhibitors,Modulators,Libraries In diploid larval cells, e. g. brain cells and imaginal disc cells, the GFP CP190 BTB D protein exists as speckles and co localizes with mRFP CP190. These results indicate that this N terminal Cp190 fragment is sufficient to associate with most of the Cp190 containing insulator complexes in living cells. Although it associates with all Cp190 sites, GFP CP190BTB D, like the CP190dC, is not functional in the insulator complexes and lacks essential Cp190 functions. y2 w ct6, P, CP190H4 1 flies have the same y2 body cuticle pigmenta tion and Cilengitide ct6 wing shape phenotypes as the y2 w ct6, PCP190H4 1 flies.

The GFP CP190 BTB D transgene also does not rescue the lethality of homozygous CP1903. From at least 500 F1 offspring flies of the y2 w ct6, P, CP1903 TM6B, Tb parents, we obtained no CP1903 homozygous adults. The mRFP CP190 redistributed to extra chromosomal spaces during heat shock whereas Rapamycin Sirolimus the CP190BTB D fragment remained associated The heat shock response in the Drosophila melanogaster has been intensively studied. When fruit flies are stressed with heat, the transcription of most of the nor mal genes in cells is shut off and newly synthesized RNA species correspond to a small number of he

be done by brute force, there are n! permutations of the vertices

be done by brute force, there are n! permutations of the vertices of a graph with n vertices. Each permutation corre sponds to a possibly unique adjacency matrix. The adja cency matrices can be linearly ordered by considering each matrix as a binary string of length n2. The first such string can then be chosen as the canoni cal label for the given graph. The problem with this method is that inhibitor supplier it involves produ Inhibitors,Modulators,Libraries cing and sorting n! strings. For example, let G1 be a graph with five vertices, v1, v5 with edges between Inhibitors,Modulators,Libraries vi and vj if i j �� 1 modulo 2. Let G2 also be a graph with vertices v1. v5 but with the edges vi, vi 1 so that we get a 5 cycle, together with an edge connecting v1 and v3. See Figure 6. Both graphs consist of five vertices, two of which have degree 3 and three of which have degree 2.

Thus, by only looking at the degrees of the vertices of these two graphs, we can not distinguish them. On the other hand, the graphs can be distinguished by finding the equitable partition of the Inhibitors,Modulators,Libraries vertex set for each graph. The unique coarsest equitable partition for G1 is. Each vertex in the first cell is connected to three vertices in the second cell, and none in the first while each vertex in the sec ond cell is connected to two vertices in the first cell and none in the second. On the other hand, the unique coarsest equitable partition for G2 is. Here, each vertex in the first cell is connected to exactly one vertex from each of the three cells. The ver tex in the second cell is connected to two from the first cell and zero from the third.

As these two equitable par titions have different shapes, G1 and G2 cannot be isomorphic. In general, equitable partitions are insufficient to dis tinguish between non isomorphic graphs and therefore insufficient to determine canonical labels for graphs. They must be used together with individualization, which can be described as follows. Inhibitors,Modulators,Libraries Suppose the partition P is not discrete, then let C be the first cell of P with more than one element. Pick an element x in C and consider the partition P formed by replacing the cell C with the two cells C\x and x. P is a refinement of P, but it is not necessarily equitable. Thus, it is necessary to find the equitable refinement of P. Continuing in this manner, it is possible to individualize and find further equitable refinements until a discrete partition is reached.

As the individualized vertices Batimastat were chosen at random, the procedure must be repeated for each possi ble choice of vertices. In this way, several discrete parti tions are produced, this is the individualization and refinement selleckchem Brefeldin A procedure used in many canonical labeling algorithms including Nauty. To finish, the algorithm must select a canonical discrete partition from among those produced by the individualization and refinement procedure. If a graph has a small automorphism group then the individualization and refinement procedure will produce only a few discrete partitions, in this case it will be rela tively easy

of a component in an ancestral taxon was also inferred if ortholo

of a component in an ancestral taxon was also inferred if orthologues are present in at least one representative of its offspring and in one of its ancestors. Inhibitor kappa B kinaseb is a serine threonine protein kinase, which is critically involved U0126 molecular weight in the activa tion of transcription factor Nuclear Factor kappa B in response to various inflammatory stimuli. I B, an inhibitory unit, is responsible for retaining NF B in the cytoplasm, for the degradation of I B by phosphorylation, and for ubiquitination to translocate NF B into the nucleolus, leading to transcription initia tion. IKKb plays a crucial role in the way of canoni cal NF B pathway, which phosphorylates I B protein and thereby translocates NF B into the nucleus and initiates pro inflammatory gene transcription.

The canonical NF B pathway is well recognized in chronic inflammatory diseases and inhibition of the IKKb enzyme by a highly potent inhibitor has remained the primary Inhibitors,Modulators,Libraries goal for anti inflammatory drug discovery. The IKK complex comprises two catalytic subunits, IKKa and IKKb, and a regulatory subunit, IKKg. Although both the catalytic subunits can catalyze the phosphorylation of I Ba, the IKKb subunit seems to play a dominant role in the canonical pathway. Further more, IKKa has a crucial role in mediating p52 activa tion through the non canonical pathway. IKKa can form an alternative complex and its function is required for the Inhibitors,Modulators,Libraries development of the lymphoid organ and the maturation of B cells. Ter mination of the canonical pathway by inhibiting IKKb is a potential target in anti inflammatory drug research.

Recently, the virtual screening method is playing Inhibitors,Modulators,Libraries an increasingly important role in drug discovery. The structure based method involves docking of small mole cules and ranking them based on their score. Every scoring function has its own inherent limitations, and thus, there is a high chance for reporting false positives. In order to minimize the risks of using a structure based approach, additional Inhibitors,Modulators,Libraries filters have been used to enrich the VS scheme. The application of various com putational filters in the VS cascade certainly alleviates the difficulties encountered during the initial stages of the drug discovery process. Every model used in the VS scheme has been meticulously validated by test sets that are not included in training the models.

In general, the performance of the model is highly dependent on the choice of the ligand that used to train the model. Results and discussions 3D QSAR pharmacophore model Among the 10 Anacetrapib pharmacophore models generated, model 1 was considered to be the best, because it has the low est selleck chemical RMSD value and a high correlation coeffi cient between the experimental and estimated activity data of the training set. The difference between the total and the null hypothesis cost is 40. 21. If the dif ference is 40 60 bits, then there is a 75 90% chance that this model can represent a true correlation of the data. Additionally, the difference between null and f